I'm 20 and I have a problem that I've been meaning to get some clarity on. During sexual encounters, when I ejaculate, I have trouble getting another erection usually taking between 15-30 minutes. Also, if I don't have sex for a week or two, I ejaculate very quickly within 2-5 minutes. However, if I continue on to a 2nd and third time( still waiting to get an erection in between those times) the time does get longer for the 2nd and on the 3rd time it's especially long but most times I won't ejaculate and lose my erection. Can someone explain to me what's the problem?