I masturbate and i do it for a longer, means by watching porn for a while. after masturbation where is pain in my legs and stiffed for next 2 weeks.

Uncertain Q?: If by "longer" you mean hours, and your legs are in the same position for that entire time, that might create the pain and 'stiffness' you describe. In any event, it sounds as though you need to change something--likely your position every few minutes while distracted. Also, be certain to not let it interfere with a normal social life.