One of the hardest things to do is to separate sexual abuse from sex itself. Personally, I dealt with alot of guilt and shame because when I finally did have sex and was arounsed and enjoyed it, I thought it meant that I had enjoyed being abused as well. I didn't understand then that my body had gone through the physical act of arousal to protect itself and that one did not equal the other. Amazingly, it took a male friend of mine, who had also been abused as a child, to help me sort out my tangled mess of a mind.
As for the sex itself, you said you get aroused, but some positions hurt and make you tense up. Can you try other positions or acts that don't hurt? Does your partner know what you experienced? Can you slow down and remain in some "happy medium" where you're doing something sexual that you find pleasurable, but not progressing into acts that trigger you?
at 2:23 PM on Dec. 9, 2010