Teething?

Hello FTM here...How do I know if my baby is teething for sure? He’s been super fussy the last couple days. Crying ALOT and sometimes really bad like he’ll be nursing and then just start screaming! I don’t see or feel anything in his mouth but I’m just not sure. He will also chew on his hand sometimes. He hasn’t been able to sleep much longer than 10 min during his naps(not sure that needed info but yeah) I just am not sure. He just turned 3 months yesterday(10/3)

He was crying as I took this picture