How did you know your baby was teething & how long before the tooth came in?

I’m at a loss of why my baby has been SOOOO fussy the last few weeks which isn’t like him. He cries all the time and occasionally rubs his ears but there’s no temp or any other sign of an ear infection. He does chew on stuff but no like a crazy non stop amount. He’s 5.5 months by the way. I’m a FTM and idk if he’s teething or what! His night sleep has been the same, 1-2 wakings. Naps have been a little worse but that’s it. We’ve already gone through the 3-4 month sleep regression.