Some of the parameters you've sketched out are ambiguous, like what exactly you mean when you say the opponent didn't "move" (do you mean didn't change squares, or didn't take any actions?), and what you mean by "in a round" (do you mean on your turn, or do you mean from the beginning of your initiative count in one round to the beginning of your initiative count in the next round?).
The strict reading of what you've written is that you made all three attacks on your turn, and it goes without saying that the opponent took no actions because, after all, it wasn't his turn. But I suspect you have a less strict reading in mind.
For example, one less strict interpretation is that you have Improved Trip, and you have convinced your DM that when you make a trip attack with a weapon you get to add sneak attack damage (even though the trip attack itself doesn't cause damage, it is a technically a melee attack). Thus, you made a trip attack, succeeded, then made the immediate melee attack you get from Improved Trip, then when he tried to get up you took an AOO against him.
The strict reading of what you've written is that you made all three attacks on your turn, and it goes without saying that the opponent took no actions because, after all, it wasn't his turn. But I suspect you have a less strict reading in mind.
For example, one less strict interpretation is that you have Improved Trip, and you have convinced your DM that when you make a trip attack with a weapon you get to add sneak attack damage (even though the trip attack itself doesn't cause damage, it is a technically a melee attack). Thus, you made a trip attack, succeeded, then made the immediate melee attack you get from Improved Trip, then when he tried to get up you took an AOO against him.