once doctors run blood tests and everything comes back normal, doctors barely help with erection problems because they can only talk what they learned NOT what they experience. yea doctors can help but to say "they can you help you far more" than us people who are actually experiencing stuff like this is an overstatement.
It's time to see a doctor. I am not saying that to scare you, I am saying that because the doctor will help you far more with this than any of us.
No offense to those trying to help him.
Well you say it never happen before meaning you don't have a history of doing it so it could be a mild case of performance anxiety. In that case, if you are over age, a nice alcoholic drink may loosen you up.
Option #2 could be refrain from masturbation for a while. That's if you are masturbating constantly... That could keep your sex libido down. Stay away from it for a good week to make sure that is not the problem.
If neither of these can help, please provide more details as to why you are not getting an erection with this particular woman.