I used to be on wellbutrin, not only did it make cigarettes taste horrible (im a smoker) but it also made me lose pretty much all interest in sex. But having sex can actually increase your sex drive. Sometimes when Im not in the mood, my boyfriend and I will fool around for 5 or 10 minutes and I will get in the mood. Maybe if you just approach her like that playfully it will get her wanting it. And, not surprisingly, the more you do it, the more you want it lol. I also agree that you should bring it up and see how she feels about it. It could be something completely different thats affecting her moods and it could be something fixable. You wont know until you ask