29 weeks pregnant and my back teeth hurt only on one side mostly when i wake up what could be causing this?

Many things: Sounds as though you need a dental evaluation. It could be anything from wisdom tooth to abscessed or decayed tooth to pregnancy gingivitis. See a dentist asap for evaluation and treatment

Tooth pain.: You need to see your dentist as cavities and gum disease are more common in pregnancy.

Please see Dentist: If you haven't seen your Dentist since before you became pregnant you're overdue. Problem could be anything from clenching to abscess (infection) to sinusitis, to gum disease, to sinusitis, etc. To be diagnosed you MUST see your Dentist now. Once the cause has been established, the proper treatment can be administered. Please call your Dentist.