No, there's nothing wrong with you. A lot of guys don't want to admit it, but it happens more often than you'd think. Guys usually have trouble getting an erection when they're nervous, scared or worried about something.

They might be afraid about getting their girlfriend pregnant or getting a sexually transmitted disease. They might be worried about how they'll "perform," or they could be feeling guilty about having sex. Drugs (including some anti-depressants) and alcohol can also prevent you from getting and maintaining an erection.

If you can get an erection when you're alone, then you're probably worried about something when you're with your partner. Think about how you feel and then talk to your partner about your concerns. You might be putting too much pressure on yourself, or not protecting yourself by using condoms and birth control. Or maybe, you'll discover that you're really not ready for sex right now and need to wait until you're older.

And remember, the idea that you can ejaculate (cum) and get another erection right away is a myth for most guys. Usually, you have to wait a while. This is called the refractory period. It can last minutes, hours or days, depending on a guy's age and health.