I think many people consider missionary position to be the premature ejaculation position. I would say it's a little bit unusual, but nothing to be concerned about. We all have things that work for us and things that don't.

I would not worry about it, look at all the positions that do work for you...

One thing to consider is how close to the brink or the point of no return you are when beginning intercourse. Many fellas nowadays operate under the misguided misconception that the best way to an orgasm is from lots and Lots and LOTS of stroking/thrusting. WRONG. If this is your approach, the recommended strategy is to make out and fool around {Necking, Petting, Heavy Petting, and Foreplay activities) to build your level of arousal to a level just before losing control, first.

If you are at peak when inside yet still cannot get to the trigger point of a climax, try shifting around in order to generate more friction. Another recommendation is to try different positions. A third method to try is for your partner to continue stroking the shaft while you stroke/thrust.

If you click on the site's Home Page you will find a section devoted to illustrated sexual positions that are animated. Look at them, find a few that interest the two of you and give them a try. If some modification is required as noted, experiment.

I hope this is of help. Got questions?

-doc

P.S.

Here is a fourth method to put forth and try:

"Playing Ball" and How To Tips for Prostate Massage

Without knowing more about what you are experiencing it is difficult to give a definitive solution to do. The information in this article discusses prostate massage and a judicious squeezing of the testicles. Both actions will dramatically increase a man's level of arousal when done when he is near the brink of an orgasm. Rimming is also worth trying. Stimulating the outside of the anus as well as just inside after becoming very aroused will also help jump start an orgasm.

At the very least, all three feel really really good when done appropriately--and not too early into your arousal building. As noted, save all three for when you are near the point of losing control yet can't quite get past the point of no return.
This is also an excellent tutorial for people interested in and concerned about the how-to of Anal stimulation as well as play.

every guy is different and every pussy is different. Find what works for you and enjoy. If some position does not work then dont do it.

Try sitting up more. Laying full-length over her body doesn't get the best angle, in my vast experience, while a more vertical body position works wonders!