Jazz is a perfect storm of pre-teen boy eating habits/self control, food being the only joy in his life, estrogen pumped castrated male body and now being full of psych meds on top of everything else. Psych meds can cause huge weight gain. In addition to weight gain due to messing with your metabolism, some psych meds can actually cause compulsive behavior like gambling, shopping, and binge eating.
Powerlevel: I've personally seen someone of normal weight and eating habits switch to Abilify and gain over 60 lbs within a few months with no end in sight due to binge eating. I once saw them stuffing their face uncontrollably just like Jazz. They had just finished a big meal, finished everyone else's plate and then I walked in on them in the kitchen shoveling in the leftovers. It was horrible. Once they switched meds again, it went away.
The point is while I can't say for sure anti-psychotics are causing Jazz to balloon up/binge eat they most certainly can.