I tend to agree with you that it may be all mental. Please take Lara's advice on your Neorologist? Thread, where you ask for places to speak to a Psychiatrist, although it may be a Psychologist you need.
Tell me, if you will as you are being so open as you get to know us, do you have thoughts or feelings of guilt when having - or after - sex? Guilt that something so nice shouldn't be happening to you?

Dave.