D&D 5E How to deal with Metagaming as a player?

Hello there! I play in a party as a rogue (LV.3 Assassin) and my companions always try to Meta against me. For example...

We were camping in a forest while they sent me to be the errand boy and gather some wood for the fire. Instead I did a recon and found an old man. I spied on him and he ended up being some kind of warlock. He summoned a strange blade with some kind of ritual (didn't conjure it) and I thought it would be a good idea to gather intel on him and steal the dagger.

I slightly stabbed myself and shouted. The old man came to help. We sit down his camp while he treats my wound and we talk. After a while my companions start searching for me. They spot me from a distance, talking with a hooded figure. There is no way of them knowing who he is or how he looks.
Then one of them shouts, "Did you kill the old man yet?". We end up fighting him and I'm falling unconscious. The old man was a leper and after the fight one of my companions intentionally threw his body over me and looted me not checking if I was dead or alive.

After that I wake up and try to find a cure or something. I end up in a small village and I'm trying to raise money to find a cleric and heal me from leprosy. I cheat in a gambling game in a tavern and I end up getting cought cuz I rolled poorly. I then proceed on making a run for it and my companions spot me. They end up massacring the whole tavern and I end up falling unsonscious again. When I wake up I'm tied up on a horse and when I asked my companions why they did that to me and why the left me for dead they replied "We don't trust you cuz you caused a fight in a tavern", which is partialy true but there was no way of them knowing that cuz I whispered to a waitress that one of them had a mental illness so that she doesn't call the guards on us cuz they were hitting on her.

This is some I have to deal in every session. They always try to up with me, slip me roofies and mess up, and I always end up throwing CON saving throws cuz I try to roleplay. How can I protect myself from that. I tried calling on them to the DM but he says there is not much he can do about it...

* UPDATE *

As people seem to not fully understand the situation I think I might add some info.

I think my alignment as the character would be chaotic good given my backround. My character grew up with his mother that was a prostitute and she was murdered by a strange cult of nobles that were in town at the time being. The assassin was witness to the so called murder but there's some mystery to it, leaving a slight possibility that my character's mother is still alive, therefore my character has become an assassin that goes after nobles in the hunt of info about this strange cult.

The other players, 4 out of 5, including me have never played D&D before. Only me and another guy are avid RPG fans. The other two have never played an rpg in their life, actually one of them constantly tries to cheat with the die and have free rerolls etc etc... The other one just sits during the whole session and joins in battles. He is not a problem at all.
Now on the playstyle, we do have a difference of opinion as to how the game should be played. The guy that tries cheating has told us that he doesn't like "talking" he just likes the fights (He made an evil Paladin that wants to be Heisenberg by making drugs). In fact, during the last session he betrayed us to someone and I forced his tongue (I literaly exploited his inability to roleplay) and we are mid-fighting. I pretty much enjoyed that.

That's not "metagaming", that's just playing in a player vs. player mentality.

The only solution for it, especially if the DM won't step in to mediate, is to find a group of players that are looking for the same type of game-play experience that you are (i.e. ones that aren't looking to answer you doing things they don't like with them doing things that you won't like).

Well, first step would be to tell them how you feel and how their actions remove any possible enjoyment you would have from gaming with them. If they are good friends, I guess they should listen to what you have to say at least.

Now, how comes your companions have access to roofies in a fantasy game? I mean, if the Dm introduce some stuff like that, he's more or less encouraging this kind of play.

You say something like, "Guys, the way we've been playing isn't very fun for me." Then you give examples of what you DO find fun. Then you ask if they'd be willing to play that way. If they say "Yes," great! If they say "No," then find another group.

The DM is right that he can't do much about it. The DM has no more social power than any of the rest of you. His or her power exists only in the game world. It's on you to communicate how you want to play and, if you're finding no satisfaction in that regard, to find people who do share your interests and play with them instead.

Ok, how old are your fellow players? Have they played a lot?

It sounds like there's no DM at all?!

I agree with the above posts.

Where I disagree is that if you don't feel comfortable talking to the whole group, you may want to talk to your DM first (in private). Explain that the game is no longer fun for you and that something needs to change.

The DM is the one in control, and he always has the option of shutting things like this down - a simple "no PVP" will suffice. Personally, I have several rules such as no evil characters and the old standby "don't be a jerk". Your fellow players are being jerks.

You may have already tried that, you need to be very explicit on whether or not this is a deal breaker for you and explain why.

However, not knowing the dynamics of your group there's only so much that we denizens of the interwebs can help. Ultimately you have to decide if this group is right for you and if it's not you need to get out of there. The game should be fun. If it's not fun you may have to find a different group.

Good luck.

I know it's difficult, but pluck up the courage to talk to the group as other posters before me have said. I know from experience that his can be a very daunting prospect. But once you have told them that their behaviour is not enjoyable for you, closely judge their reaction.

I played D&D in one group every week for nearly a year where I wasn't entirely happy with what was going on but didn't say anything for fear of not being able to play D&D. I was thoroughly miserable playing something that I was desperate to enjoy.

My game fizzled out eventually but looking back, I wish I had said something to them. Admittedly, my scenarios weren't as harsh as yours, and these days I will say something straight away, even if it accidentally upsets someone. Your Gaming life is too short to be unhappy playing.

You have to address this to the group. If they will not change, there are thousands of new gamers just waiting to join up with others like you to play the beautiful game

I hope it works out for you.

Step 1: Add some paragraphs to your text. White space is your friend. Help us to help you - by making things readable.

Step 2: Eh. Normally I'm all for talking it out, calm rational debate but heck - sometimes you've just got to call for a long rest then murder every other character during your watch. It won't solve anything, but in The Game of Dickery, practice makes perfect.

Also, get your DM to grow a pair (...of fair, kind-hearted, eyebrows).

If Beavis and Butthead played D&D with Stewart as the DM..."Go get some firewood, Beavis" "Hehe. Yeah. Firewood."