Hello Doctor Everyone Say Masterbating Will Not Effect Future Sexual

Hello doctor everyone say masterbating will not effect future sexual life and they also say its healthy...then why I feel tired after I shag and also I feel joint pains....and I have a another question it takes 15mins for a girl to reach orgasam.. But I shag not more then 2mins is that because I am been shagging from childhood... If its wrong and effect us please do let us know instead saying healthy & other things...