Check out resources online that discuss exercises you can do. Bring them into your OB and see what they say. I found that stretching gently, being on my hands and knees and arching and rounding my back helped.
Also, invest in some pregnancy massages through a certified therapist who SPECIALIZES in preggo massage and maybe even has one of those tables with the cut out hole.
Pregnancy is a medical condition, not just some fact of life you should be expected to endure. Do what you need to, to take care of yourself.
I had such bad back issues after a car accident that my husband bought me one of those massage chairs/pads for Christmas. I used it a lot during my third pregnancy. It was PRICELESS. I would soak in the tub, then get comfy in my "chair". It helped me to relax, my muscles to stretch and expand, and for me to get some much needed rest.
Oh yes and check out Water Exercise Classes for pre/post baby. They allow you to move in an almost weightless environment that you simply can't on land. It's only for preggos so you don't have to feel selfconscious about getting into a swimsuit. I taught and took these classes. You can move your hips and legs like neverbefore!!! Plus I really think this little bit of exercise helps you to sleep better. And it's really nice to have other preggos who are "suffering" like you and have a lot of the same questions as you to talk to and look forward to seeing every week!
I hope you find some relief.