Sorry to hear that! That's really mixed feelings.
Well I think meds can make a big diference in the weight you gain. For exemple people treated with mirtazapine increase their appetite a lot. By my side I'm for the first time of my life knowing what feels not having appetite, I blame it a little bit on my meds, cause before them I used to eat a little bit more, that I need, and want, and, should...Depressions also can make appetite increase.
May you could talk to your doctor about that, if you have one, and have meds adequated to your circunstances.
I think I can not give you much more usefull advice. My wheight never changed too much. But somedays I would eat even if I had aches or felt full. By know I'm somehow happy I don't have as many appetite has I did.