I'm a fairly open 21 year old guy. I'm not shy, I love being naked and I'm totally comfortable with my size. However I've noticed that I find it quite difficult to maintain an erection at times when others are around. I've never been in a situation where I've had to get it hard in front of anyone except during sex - however even then I find it difficult to maintain, particularly when I put on a condom. It's not like I don't feel sexual, I literally just can't get more than a semi. It's not only limited to erections - I can't really use urinals because the second I flop out my cock it's like I've lost the ability to pee. This also happens when I'm alone sometimes, for example when I was taking pictures to put on this site. I'd get rock hard but then the second I lifted the camera, I started going limp again. Is it nerves? Am I covering up true shyness? What is it?