Suddenly very fussy at 3 months

Addi • Baby #2 due Jan 22!
I'm at a loss. Baby boy is 3 months old and suddenly rather fussy. Sometimes he'll just gnaw on the bottle or push it around with his tounge. He's super interested in putting anything in his mouth, and will chomp on my fingers. Could this be early teething or is that just normal development? No fever, no runny nose.... I'm feeding him on demand... I just don't know.