I had, and have the exact same problem, all guns are balzing and when its time for the raincoat... nothing!
For me I think its in the head, I had a bad experience with someone I loved, at that time I didnt think it would impact me, but it has, for a very very very (way to very) long time I had problems.
Tried porn, worked partially, I dont really drink, also relatively healthy so I eventually went to the doctor, she gave me viagra and the problem was solved (a new everready problem was however introduced), but I wasnt happy with the solution. Im 25, I should have these problems right?