Hello dr, I am 19 years (male) and I have a problem with my penis. I have excellent erection every time and when with my girlfriend, we do foreplay and my erection is hard but at the moment that I remove clothes to penetrate, I loss erection, it comes and goes directly alone and at the end when we are done (no sexual intercourse of course), I grab her from behind and have large erection again. I don't understand what is happening. With clothes on, I erect. When naked, it goes and when gaining back clothes, it erects again. Please help me, I am so young and I am unable to have sex. I want even to cry. Please help me with both detail information and treatment if necessary. I don't smoke I don't drink alcohol I do a lot of sports I am healthy I don't know why my erection disturbs only at the moment where I remove my clothes and when clothes on, it erects fully.