J.S.
I was actually talking with a friend of mine about this a few weeks ago beause she had a similar problem with her son. Her dr. made this suggestion: Instead of draining one breast at a time, switch before your breast gets, umm soft & squishy! He told her that when her boob loses its fullness, it can cause them to start biting, or gripping firmer. So, she said she started switching earlier and it has helped tremendously!
Not sure if this helps or not, but just thought I'd share it with you!
Good luck!!