In the past year I've gained 30-40 lbs, especially in my...

Hi, I think it might not be fatigue as much as a lack of motivation to exercise. Of course, you understand that in order to lose weight you need to exercise and eat properly, but maybe you haven't found the combination that suits you best. I suggest maybe going to a coach and figuring out which sport you like to do the most. It also took me a long time to understand the type of sport I want to do, but since then I've really persevered because I really enjoy it.