Have you considered a prescription like Viagra or cialis? Just a little boost until you gain confidence?
Maybe watching porn while you have sex, unless that is an absolute no go for you.
Maybe getting your partner to talk dirty to you or start you off with her mouth to get you going.
And finally I am going to ask you, please don't take offense: are you attracted to women?
I don't know if any of this helps, but I wish you luck.