Liam started drooling heaps at around the 4 month mark, but didn't get teeth until 8 months. I think that the drooling can just be another development stage they go through, although drooling can be another sign of teething. You'd have to be a bit unlucky to hit teething this early though. We used heaps of bibs each day, cos he would just get drenched otherwise.

Hope your little man gets better soon.