I am in my mid twenties, and have minimal sexual experiences

Here is description of the problem:

1. I can get and maintain a erection given stimulation.
2. I cannot and have never masturbated to climax.
3. Someone giving me manual sex cannot help me achieve climax.
4. I have wet dreams and can climax there.
5. When I get really excited (e.g. when watching some porn), I release pre-ejaculate.

I do not get the climax feeling when awake (different from not ejaculating but climaxing). Whenever I'm with my gf who gives me HJ's, I get really aroused and stay erected for a long time but can't climax. This leaves me very frustrated because I can't sleep when I get home (due to excess horniness that is not released). I think there is are some sensitivity issues with my penis. Is this condition pretty common? Especially the insomnia part?