Trouble staying hard during sex
I have no problem getting hard for sex, but about 5 minutes into the sex I go soft and can't get hard again, even though I still want to have sex. Sometimes I go soft because I think that I'm not performing well enough, other times I feel the orgasm coming but I try to hold it in, and when I do I feel a sharp pain shoot back inside me and it makes me go soft. Then there's times when I go soft and I have no idea why because I'm still horny, I just can't stay hard. I'm very attracted to my girlfriend so I know that's not the problem. Does anyone know what can be causing this or has anyone experienced a similar problem?
BTW I am 19 years old.