I haven't heard anything like that being caused by Prozac (though I have no experience with it).
My advice would be to just get back in the gym, switch up your routine to something you enjoy, and just have fun with it. Don't worry about the mirror or scale for a while (easier said than done; believe me, I know). Do this and focus on eating enough and good foods and just run with that for a while.
It seems like simple advice, but just try not to worry about it and be happy, bro.