I would have suggested the h2o2 like you are doing... have you tried a netti pot? give it a go with a saline solution... I use sole in mine and then add a drop or two of Lugol's in it (about 1.75 pints of water). Do NOT use more Lugol's than this or it may sting...
Are you oil pulling? Do you use a drop or three of oregano oil in the oil pull? If not, that would also be something to consider...
One more thought... rinse your mouth out and gargle with a strong salt water solution several times a day.