It isn't easy...
I used to run my own campaigns every other week, working on them in the days prior to game night. I have a full-time day job, too. Once freelance assignments started rolling in, I had to make time to write. I'd do it at work during my lunch hour, for a couple of hours each night after I got home, and for several hours more on the weekends.
I found myself running game sessions more sporadically, or not running any games at all, which was a pain because I was the only DM/GM in my group. That meant that I wasn't getting much, if any, game time. I managed to find another play group, but they run on a weekly schedule (every Friday, 6pm til the game ends, which is usually between 1am and 3am). When I'm on deadline, those long weekly games can be hard to commit to.
These days, I've got a three month old son that contends for a good portion of my time. So much for the regular game nights; I make one out of every 3 or 4 sessions. The guys in the group are extraordinarily forgiving of these absences. The weeks after my son was born were probably the hardest -- my word count dropped, and although I was happy with being a new father, my self-confidence in relation to my writing and design work was on the ropes.
Once I started making time, exhaustion or not, things got better. Those writing "muscles" need to be worked regularly, preferably every day. Not writing is a sacrifice that I can't afford to make at this point. I've got a decent day job, and my wife works part-time, but the extra money I get from freelancing (sporadic as it may be) really helps the ends meet with a little more surety, especially with the cost of living in SoCal.
I have to say, it's tougher some days that it is others. Gods know that I should be writing now, at this moment, instead of posting on EN World, but the topic was too close to the heart for me to ignore.
Gary