I do a very minimal weight lifting routine 3 days a week, and a low-mid intensity 30 minutes on an exercise bike every morning. The weights are like a 20-30 minute workout that takes me an hour because I hate it, I hate doing it, it never makes me feel good, before during or after. I basically accepted the fact that I'm never gonna have the motivation to be Mr. Muscles, but if I keep doing my minimal routine I will stay relatively healthy and that's gonna have to be good enough.
I also changed my diet a bit and switched to only drinking water. The diet thing sucks because I love junk food and such and I'm having a lot of trouble getting my weight down to where I want it (just 10 more pounds would be nice). I do not miss soda or iced tea or any of the other stuff I used to drink before switching to water, though.
Since I started this I managed to lose 30 pounds and put on a bit of muscle (not a lot, not as much as I would like) but it took like almost a year.
I kinda treat it all the same way I treated quitting smoking, like trying to beat a high score in a game. I keep a log of what exercises I do every day, how much I weigh in the morning, things like that, so I can see my progress and try to "beat my high score" or keep my "daily log-in reward streak" going. I've always enjoyed gaming so I incorporate those kinds of things into it.
Before all that crap, though, I'd make sure your mental health is in order. Mine's all a shambles but I'm giving it one last try.