I am 20 yrs old and seem to have a penile disorder

I am 20 years old. I have had issues since I became sexualy active achieving an erection during sexual intercourse and had begun to believe that i had erectile dysfunction. After some research i had come to the conclusion that it was strictly a psycololigical form. I have been working on it myself, keeping the worry of it reoccuring from entering my head during intercourse, which has given me major improvements. I have been healthy enough sexualy to have intercourse 5 or more times in as day, but the problem still occurs every once in a while, somewhat randomly. I beleive that if i keep working at it it will eventualy go away completely. But am i just fooling myself and realy should seek medical help or how possible is it that the problem can cease with my own efforts? Another related problem that was recently brought to my attention by my girlfreind of nine months is that i rarely am completely hard; i will have an erection and even achieve an orgasm but there have only been few times that i have stayed rock hard. Is this normal or is it a sign of a physical erectile dysfunction?