Terrible back pains!

Malarie • 26 years old, Married, Mother of a 7 yr old girl & newborn boy!
I am currently 22 weeks & I have a lot of trouble sleeping mainly because of my terrible back pain. I toss & turn, try sleeping in different positions but none of that helps. I don't know what to do to relieve this back pain. Anyone know of any ways to relieve back pain without it causing any harm to baby? Oh, I'm high risk for preterm labor btw!