Mine was like this when he started teething at around 3 mos. He was super fussy, drooling, bite-y, and of course barely sleeping.
Since then, pretty much every time he starts cutting a new one, he either refuses to nurse for a couple of days, or gets real bite-y. I just have to resort to pumping during the day, which kinda sucks, but oh well. During the night, he often "forgets" he's in rejection mode and will nurse just fine. And that's just fine with me. It seems to pass in a couple of days and he gets back to normal.
4 months sounds like a good time for a nursing strike if you haven't had to endure that yet. Not fun, but if you stick it out, it's worth hangin' in there for the long haul, IMO.