What do you do if the lower part of your back hurts while pregnant?

First make sure they are not contractions. Try to see a chiropractor. Most will treat and adjust even while your pregnant. Some people look down on chiropractors. If I did not go see one during my second I would not have been walking the last three months of my pregnancy. With my first I was crawling to the bathroom the last three months. They can do wonderful things sometimes. If your insurance does not cover one, depending on what state you live in, most are affordable to pay out of pocket. Call and talk to one.