I am 17 years old. I used to have problems with premature ejaculation, but that mostly subsided. I had a girlfriend last year who I was very comfortable with but couldn't  keep an erection. I guess this fed into a bad cycle, but I thought I got over it. More recently I tried having sex with another girl, and again--I could not get an erection. All through foreplay I was good, but as soon as it was actually time, my penis just went kind of limp. So I tried to move past this emotionally; I think the problem stemmed from when I tried to control my premature ejaculation and I held back too much and found it too hard to get an erection. I am now with a girl and I have been trying to let myself go and keep my erection going, but I have started ejaculating prematurely again. This is a ridiculous cycle. I don't have any health problems, I dont take medication, I drink and smoke weed infrequently. Any insight as to what the problem is or how to fix it?