I'm 18 and i've recently started a relationship with a new girl friend, approximately 3 months. Up until 3 days ago, i've had erections that were extrememly hard, and would never go down, but three days ago, we decided to move ahead and begin having sex. I was fine until i removed my pants, then as i was about to penetrate, my erection disappeared, and would not return. We've tried the subsequent 2 nights, but to the same result. I am worried. At only age 18, i didn't believe that i would have a problem with ED. I clear my mind each time before we attempt to have sex, but as i said, the same result comes. please help me, I want to satisfy my girlfriend.