I am 17 years old. I have been masturbating almost daily for the past 3 years. I DO not MASTURBATE IN THE NORMAL TECHNIQUE. I MASTURBATE LYING ON MY STOMACH AND MASSAGING OR RUBBING MY PENIS.(HEARD FROM INTERNET, ITS CALLED MASTURBATION PRONE TECHNIQUE) For the last 2 years, my erection lasted longer, my penis size without erection was almost twice bigger than now. Now I get erection only with physical touch (earlier it was not necessary) and too lasts only for a small time. I do not smoke or drink. IS THAT KIND OF MASTURBATION LYING ON STOMACH HARMFUL? So please answer me why it happens and what I should do to rectify it?