my dp was exactly the same. we dtd probably about 5 times throughout the whole pregnancy.
i could never get my head around it, took it really personally and felt very rejected. i tried to get him to 'explain' it to me several times, but he just said he felt weird and that he felt like he would poke the baby in the head!
anyways.....just wanted to let you know that you are not alone, and for us, it never turned into a permanent problem. once ds was born dp went straight back to how he was before the pg.
hth