You have a strong pain in your penis so you can't stand it anymore and finally you decide to go to the doctor to see what they can give you to solve your problem. The doctor is surprised to see that your problem is a BIG one (literally your problem is that you have a permanent erection) and even more surprised to see the doctor's eyes that denote that she is a whore and she wants you for it. You are left with only one option to make it all work out so you can both be pleased; she has sex with you to get you off and he cures her pain. It's a win-win.