Why do i freeze up when im touched?

I have been engaged to my fiance' for a year now. we have a 6 month old son, and another baby on the way, So its not as if we're new to intimacy. but ive noticed lately that i stiffen up, and start to panic whenever we are about to make love. i love him. im very attracted to him. but its also very painful. i get very sore and raw. we have tried using lubes but we have to keep re-applying every few minutes because i dry up so quickly. i have been sexually abused in the past, but its never really affected me, so i dont think that has anything to do with it. sometimes, he speeds up a little to make it better for him, and i start freaking out. he has slipped out a few times and went a bit lower than intended causing tremendous pain, so i get scared when he does that. sometimes when i freeze up I feel like im afraid. i have no idea why. he has never hurt me. i have no reason to be afrain what the hell is wrong with me?!?!?!?!