can't get an erection.

hi, I am 16 years old and I've been watching porn since i was about 13 I would say. And when i started it, it wasent that often that i did it untill I was about 15, I was doing it more often. some times 3 times a day, sometimes just once a day everyday, times varied but i guess it was still a lot. i grew a desire for more extreme porn after a while and the regular porn i watched wasent pleasing me as much.. so now i stopped, its been almost 2 weeks since i've watched porn and masturbated; but when i tried having sex with my new girlfriend it was very hard to get an erection. i got one but it was not as stiff and when penetrating my erection didnt stay as solid enough to even continue having sex. it only got as stiff as it does when i watch porn while she was giving me oral sex and even then it took a while to get it like that. on top of that as soon as the oral sex finished my erection kind of died. but what bothers me is when we are foreplaying with clothes on not thinking of having sex i get an erection and it remains there. but when it comes down to sex it is difficult to maintain an erection. i dont know if it is the porn or what? i dont watch it anymore after what happened and will not go back ever.. i want some tips or advice on what my problem may be and how to overcome it. I am 16 years old THIS SHOULD NOT BE HAPPENING! that bothers me soo much. So please I need some advice or word of wisdome, will i recover from watching all that porn and how do i do so? I'd appreciate some advice greatly.