I can't stop biting my back teeth and it is making my mouth and jaw sore. ideas how to stop?

3 main reasons : There are neural reflexes that cause clenching associated with reduced oxygenation from airway issues. Also there is reflexive clenching and/or grinding associated with pain and/or inflammation signals being sent to the brain. If you can reduce those signals by diminishing those 2 issues, the biting issues generally diminish. The third reason is associated with stress/anxiety. Address that too.