Help!

I've posted in a few groups on facebook and haven't really gotten much advice. Has anybody else experienced this with their little one. I never did with my first. Litle guy just turned 4 months today and for about 2 weeks, he has been violent while feeding. He chomps down then pulls back hard. He does it over and over until i just decide he is done eating. I doesn't seem to be related to milk flow. He does it during all times during the session and his mouth will.be full of milk amd he will let it dribble out. He is not visibly teething, however, they are moving under the gums right now. I dont think it is gas, stopping to burp does nothing. Does any other ideas about what is going on or how to cope?