Does musturbation increase fat around my belly ?

No: Not unless it makes you eat more calories and do less exercise. Normal men, women, boys, and girls masturbate (it's universal). It is not harmful, as the body goes through similar effects during regular sex with a partner (but too much of anything may become a problem). Masturbation does not stunt height, cause acne, make you weak, create heart problems, lower fertility, change your weight, etc...