I'm 17 weeks pregnant and was woken up several times by sharp pain in my left lower to mid back that comes and goes. what should i do?

Back pain: Back pain is common is pregnancy. Unfortunately, you provided very little information that will not be enough to tell what this can be. Either provide more information for your condition or see your OB or primary care doctor for advice.

See OB: may be normal or have an underlying cause so see your OB

Musculoskeletal: Most sudden sharp pains as you describe are caused by spasm of muscles and ligaments, especially ones that support the uterus which is now enlarging at 17 weeks. You may have turned in your sleep and tweaked these muscles, causing the pain. Try side sleep on left side with pillow support between your knees - this gives uterus support while optimizing blood flow to baby. If not helpful, see OB.