For those that have babies with teeth already, how did you know when baby was really teething?

My little guy has always loved to put things in his mouth and has been drooling for a while already but recently he's been very fussy and crying way more than usual. He's chewing constantly and sleeping like crap. Is this teething?

Tonight, he's barely slept and is whimpering in his sleep. Is he in pain? Can I give him to children's Tylenol?