My horse used to to that, he ended up just being really sensitive. :( He just needs to be curried lightly. I made him less bitter about the whole thing by making a curry brush motion with my hands really lightly across his problem areas until he began to like it, then eased him into the curry brush again.
EDIT: My horse is girthy too (people marvel at how well this saddle fits him fyi.) I had this suggested to me, and it works wonders. When you put the saddle on, while being really matter of fact about it, don't brace yourself for repercussions, just be prepared for them and deal with them as they come. Just buckle the girth at the loosest hole, and walk him around in it for a while before you tighten it. It divided the saddling process so it wasn't this horrible thing that happened all at once, my horse seemed to take it a lot better.