The drooling and everything in the mouth is much more related to being 4 months old than it is to teething.
You've entered the 4 month wakeful! Congratulations! You are officially part of the club. 
The wakeful period applies to more than just sleep patterns, it involves their sudden awareness of the world around them. Part of that exploring is putting everything in their mouth (hands, toys, parts of your body...). It also involves them being more aware of what's going on when they feed. Latching and unlatching during this time period is fairly common, because 1) they're distracted by anything and everything and 2) they're starting to become more fussy/picky as they realize that things aren't happening the way they want it too. Which means before he might not have noticed the forceful letdown as much and now he's more like "Moo--oo--om, knock it off!" This also comes into play when the milk isn't coming out fast enough. Or at the wrong angle. Or not to the rhythm of the song in his head....