back molars are a total misery for everyone! we just gave panadol/calpol at night though not sure it even worked. there are some teethers made specifically for the back teeth, but I could not find it anywhere on HK Island when my son went through this a few months ago. Unfortunatley, I think all you can do it give TLC at night and cold water seemed to make our son feel better so we had to change his diaper at least 2 times at night as a result.
it took about 2-3 weeks for things to get back to normal.