My best friend is going through this with her 3rd pregnancy, 1st boy. Chiropractic has helped her keep things in line (like her hips and spine), which has helped the pain tremendously. It's almost how she knows she needs an adjustment again (usually every 2 weeks, she goes). Her OB also doesn't seem particularly concerned.
Also something else that could help is to somehow suspend your belly, so that it hangs away from your body a little. This could help deflect the strength of his movements against your back and organs. I know I didn't describe it very well, but I hope you get a good picture and figure out a way to at least try it :)