When do babies start teething?

Hi moms/ladies! How soon do babies start teething? I feel silly because I had my eldest (she's 6) and you would think I would have this all figured out but I don't recall since it's been awhile. My second child who is only 3 months old was doing fine until now, He has been really fussy recently. I have tried everything that usually helps soothe him. But I have been noticing he's been 'chewing' on his finger, his pacifier, or anything that comes near his mouth. And I know the difference between him sucking and looking for food and him 'chewing' on things if that makes sense. So could it be possible he's already teething??