This is not an unusual situation. There are lots of reasons that people (both men and women) find that arousal through oral sex and hand manipulation may allow for longer erections.

You mentioned that you thought you were at the peak of sexual performance at your age. First, there is nothing in your description that suggests that you aren't highly sexually aroused, and there probably isn't anything that is truly a 'peak' for many people. There are certainly periods of time when arousal is easier or harder than others, and aging can eventually diminish some of the speed of arousal, but it is important to know that sexual arousal waxes and wanes through out our life time.

Let's deal with the issue you are describing with having a little difficulty keeping an erection during intercourse. There are lots of things going on that may be inhibiting you. First, just the pressure you may feel from your partner, may put your head into a position to know that if you can't keep an erection, she will be disappointed. Once that happens, then you continue to worry about it, and it continues to happen because you continue to worry. It becomes a self-fulfilling prophecy.

There are some other things as well. First, depending on what position you are in, it is hard sometimes for the male to keep an erection if he is attempting intercourse from the top position. All the muscles in your buttocks, back of the legs and back are involved in holding your weight off your partner, and the blood flow in your body leaves the genitals and goes to other areas that need it.

You also may not have enough lubrication to keep the stimulation going. You mentioned that you usually keep an erection with oral sex - that is a different feeling than intercourse, and having a similar feeling with lots of lubrication (use some of the silicone lubricants to really lubricate the entrance into the vagina) may be what you need.

You also said that you are highly aroused in the morning. If you are having intercourse in the evening, then the body is more tired and not able to stay aroused for as long.

You didn't mention whether you were using a latex condom or not, and it may mean that you will want to switch to one made of polyurethane where there is more heat and feeling sensation that transmits.

As you can see, there are all sorts of reasons that a perfectly healthy, sexually active 19 year old may be not keeping erections during intercourse. This is not an uncommon issue at all, and one that men of all ages face at varying times. There is so much going on in our lives, that to keep a very active sex life along with our other active life is not easy.

It may mean that you will need to masturbate less when you know you are going to be having intercourse so that there is more build up of sexual tension. That doesn't mean stopping the masturbation because it is actually a very healthy activity and something that is good for your body.

I hope this is helpful, and feel free to write back with more questions if you have them.

Reviewed by Sexual Health Editorial Team