Back pain.

I'm currently 30 
weeks pregnant and my back pain is unbearable!! I missed a few days here and there of work and used vacation. The doctor says there nothing he can do, as in give me a doctors note cause he can't "prove" I have back pain. It's terrible to the point I can't even move. Should I see another doctor or is he doing the right thing?
Edited: I meant 30 not 39!