Hi.
Thanks for your query and an elucidate history and some understanding and mis-understanding about the topic under consideration.
First of all, come out of the guilt and
anxiety you look to be carrying on.
Masturbation 3 to 4 times in a day is absolutely a normal and physiological process in human being, gives you sufficient pleasure , relaxation and
hormonal balance and emotional outgo.
So no need to stop Masturbation.
This will have no side effects and you can certainly have a normal sexual life even after marriage.
As far as the question of not gaining weight: there are many other problems , either physical or otherwise that have a direct bearing on your physical development.
I would advise you to get checked once from a Physician and undergo some investigations to make sure that you are not suffering from some medical problem; if found out get treated and you will be fine.
Reduce your stressful life, try to relax as much as possible.