orgasm only with masturbation

I'll paint as full a picture as I can, with times and everything.

I am a 17 year old male, born September 29th 1990.

Puberty came around 2003-2004, and with it, the delights of masturbation. Since then I've been partaking in it increasingly, and in the four or five years since I started, on average, I'd say it was about 1.6 times per day.

At around March 2007 I started to express worries about my penis - I did some research and concluded that my foreskin and penile frenulum were too tight. I plucked up the courage to see the doctor, which was harrowing. He confirmed my suspicions and said it might sort itself out, or he could write a letter of referral to a hospital to see a specialist. I told him that I would consult him after my exams in June that year. I didn't, and still haven't plucked up the courage to do so.

I started having sexual experiences last year - the first notable one was fooling around with a friend of a friend in August 07, when I was 16 going on seventeen. Since then I have had a few more, but now since January I have a steady girlfriend. She lives some distance away, and we only see each other once a fortnight. To make a long story short, we have sex. She has polycystic ovaries (or something) which means she's on the pill anyway, so I haven't worn a condom.

This is fantastic for her (she definitely has no problems in that area) but it gets somewhat problematic for me because no matter what we try, hand mouth or vagina, the only thing that gets me to orgasm is my own hand. Granted, sometimes after we have sex and she lays alongside me stroking my body and kissing me while I masturbate, the orgasm is intense, but she can't bring me there - only I can.

This has caused me a great deal of stress and frustration. I am worried that the combined factors of my foreskin/frenulum, and adaptation to a specific masturbation sensation, coupled with general stress and insecurity associated with sex, are completely crippling me. I've reached the point where I can't hope and turn to the internet for help.

Please, I beg you. I'm at the end of my tether. What do I do to have normal, healthy sex with my girlfriend?