Chewing on nothing and sticking tongue out

My 5 week old baby has been chewing and sticking her tongue out, mostly after feeding, so I know it’s not due to hunger. She’s been doing this a lot recently. She was born with an 8mm neonatal tooth on the lower jaw that hasn’t erupted. Is this a sign of teething and her tooth is about to cut? Or is this just a sucking reflex or a form of self-soothing? She doesn’t seem to be in pain. She will just lay in her cot chewing quietly. Any advice?