Baby teething already?

my son is three months old and is already acting like hes teething. he gets fussy, but when i try to feed him he just gnaws on the nipple. when he doesnt have something in his mouth, he shoves his fist in and he doesnt suck on it, but chews on it. did anybody elses baby start teething this young? my son started at five months, and my daughter at months....