Are you circumcised? Do you wear condoms? These can both desensitize you, as well as other creams and lotions on the market. The only other thing I can think of is premature ejaculation. I'd try the other things first though, because you're still young and really just starting to have sex. PE is a manageable condition and there are still things to help out. Your best bet is to keep having sex as you'll soon enough become less sensitive.

well i guess so thats what im told but ive seen virtually zero improvement and iam circumsized and i always use condoms

After time you might last longer. I have somewhat the same problem. The first time with my girlfriend, didn't get past 5min.
After the usual would be 10min.
We had sex frequently, the average would be 10-15min which is not long compared to most guys I've heard of.
But every now and then (once a week, or once every two weeks) there would be a random day where I'll last quite a long time... 30min . Once in the past five months I went up to an hour. But that was rare. Usually I don't get past 20min.
But again, at first (the first month) I wouldn't get past 10min.
Things that affect it (from what I've noticed) are nutrition. (High zinc/wheat diet help) Exercise (cardio exercise helps a lot, running, cycling, swimming, in-line.) And most important, the position.
Doggy style usually tends to cut down time. Missionary as well, but that mostly depends at your speed. A position that I find comfortable for both of us (especially pleasing to her) that helps you last, but still gives speed, is missionary but with her legs over your shoulder (not sure what it's called.)
But give it a try.
One more thing, even though I'm not so sure this does much but it might, the thinner the condoms the more sensitive you are. So try using ribbed or just normal condoms to lower your sensitivity.
They sell condoms (durex brand) that have this lubricant that helps you last longer. Though I've never tried it, but I'm sure it works cause it's been in the market for sometime.

Hey guys I can totally empathise with you chaps, the whole PE thing is driving me insane. Check out my blog prematureejaculation.blog.co.uk it's a lighthearted look at the problem and solutions. Please feel free to add comments and words of wisdom - Craig