Hello. I am a 20 year old guy. I have been masturbating since the last 8 years. 1. I stroke it with my pants on(till just before I ejaculate)and in a lying position. Sometimes I get erect without even touching when I am in lying position. My erection goes softer when I open my pants and also goes away rapidly when I stand up, unless I keep stimulating it and doing it fast. Is doing it with pants on and while lying down a reason for this? I am concerned. To add, when I am with my girlfriend, even while making out generally over clothes, I get strong erections regardless of my posture. What is the cause of losing erection? I am extremely worried 2. I sometimes smoke marijuana. To be very honest, I do it in a very controlled way, like at a friendly get together or something. At MOST, I smoke it once or twice a week. Is this going to affect my sexual abilities in anyway in the long run? Does marijuana consumption have any effect on someones sexual factors? 3. What are the foods that I should have to last longer and have better erections? I have heard that some foods like bananna, onions and salmon increase the length of ones penis? Is that true? If it is, considering my age(20) if I consume those foods more, will I grow? I have made A huge post. Please PLEASE PLEASE, reply to each of my questions. It will be of great help. I would like to add that I am still new to some things. I am a virgin and I havent yet been involved in any kind of oral sex with my girlfriend. All I have done is made out over clothes.