What can i take for pregnancy related severe lower back pain (right side only)?

Consult: If pain is right side only and low back and does not radiate it is likely your sacroiliac joint. Si joint problems are common in pregnancy because of the stress of extra weight and increased curvature (hyper-lordosis) that occurs. See your pcp as you may be helped with a simple trigger point injection of the joint ligaments. If he does not do those injections check ortho or pain management.