These are some various reasons and solutions having to do with your condition.
First, if you are very young and rather inexperienced this may be a problem. You will eventually grow out of this once you get more comfortable and use to sexual intercourse. For now you can masturbate before hand when you know your going to be with your partner. Masturbate and have a lot of sex and monitor your progress. My partner is 27 and he is still a trigger for our first time each day. We have sex 2-3 times a day or he has to masturbate at least once because he can't last until at least the second or third time.
Maybe you are just highly sensitive. If you don't use a condom, use one it will help mask the over sensitivity. You can also use a cock ring at the base of your penis to slow your blood flow which will also help you last longer. If your sexual partners are female I know many of these come with a nub or something for female clitoral stimulation and they can be very nice for women who like to be on top. The last thing you can do is go to an erotic store and get a desensitizing cream. This is a cream that will numb you just a bit. Start with a chocolate chip size amount and put it on the head of your penis. Give it 15 min to sink in because you don't want to numb your partner. If it's not enough a bit down your main vein or boys down south should do the trick.
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