You may actually be having problems due to performance anxiety. Yes I understand you haven't had sex yet, but you might actually be pysching yourself out. I recommend that you get the physical checkup with your doctor, get the plumbing verified and all your chemical levels where they should.

I've had major problems too. I hurt my back many years ago and it has progressed to a point where I've lost the sensation of touch and temperature in my penis. I've struggled with the lost of this feeling, to the point that I didn't want to have penetrative sex with my wife because I was too upset and focused on not feeling anything. However, I've been working to accept the disability and that I can still have intimate relations without all the feeling. Some guys actually "numb" their penises with sprays and creams to keep from ejaculating. I've been able to use the problem to an advantage in that I can last a lot longer with penetration that I ever could have when I actually felt the thing. It may not seem like a lot, but I have actually successfully orgasmed through penetration three times (three separate events) in a row after almost three years without success.

My point is that it could be all in your mind. You have a lot of anticipation, and perhaps your burdening yourself too much resulting in a less than anticipated reaction from your penis.