Yikes have you told your ob? Maybe you can be referred to a chiropractor..
Try stretching, working out a little if you can (I do a prenatal workout home DVD-it's only 25 mins long) or look on Pinterest for some prenatal back exercises. Our bodies just by being prego get pulled forward and out of shape. Another thing to try is get a "maternity belly band" it supports your stomach so there is less back strain. I found mine on Amazon, but I've seen them at baby & maternity clothes stores.
All i can say it take it easy. You gotta put those feet up and rest..