Hey bro,
I go through this too, I'm quite a bit older than you and although I have experienced sex. It is sometimes difficult because of this PA that takes root almost as soon as the first time you can't get it up with a woman. For me at your age I was so scared that a girl would tell everyone I avoided it like the plague. I desperately wanted to have sex but had so much anxiety that I turned to PMO from a very young age. The best thing is that I finally know what is wrong with me and I accept it and I will, as best I can, be patient with myself. I'm 90 days in and realize now that it will take a while longer to reboot. I think it helps to feel secure with your partner so for me openess and honesty is vital but it doesn't guarentee anything. My brain is still wired wrong and changing that will take a while.... There is PA and also there is just Danny frustration from being so horny and not being able to seal the deal. This gets me into trouble so I have to be careful about my mood when being sexual also.
Anyways bro, just a few thoughts that might hopefully help. I think you should try meditating before sex. Ask your partner to do it with you. It's really pretty cool! If you don't know how to meditate try you tube or Google it.