Everybody is different. I spent 10 years on a very restrictive diet. I lost 150lbs and kept it off. Now if I eat any more than 1500 calories a day while not on gear I get fat. I have to keep my carbs very low or I just blow up.
On gear I have to be very careful to only carb up around my workouts and I grow on 3,000 cals a day. Not fast but I grow.
I have no choice to do it this way or I just get fat and sloppy.
Sounds like you need to have your thyroid levels looked at.