RHH: I think I need serious medical help?

Well Im a 13 year old boy and I went skinny dipping with my best friend Joe. The water was really cold but it was like 85 degrees out so we didnt mind. So we swam and played around a little and when I gout out, my thing was stiff. It went away later but I was watching two and a half men and it became stiff again. Should I go to the hospital or something? Im really scared.