Why is my dog's ear over waxy every once in awhile?

It's like he will be fine for 2 weeks-1 month, with slightly solid normal brownish wax that I clean out weekly, then BAM he has a day when his ears produce SOOO MUCH wax. It is very very liquidy wax that is yellow-green and looks like snot and his ear produces so much that it can get his face wet(not soaked.)He also gets really itchy ears when this happens. Usually it is gone by the next day without me doing anything(except drying his ears out 2-3x). I guess I remember him being like this every once in awhile but I just recently noticed the pattern, AND it is getting worse(more wax).