Thumb sucking!

My LO is 13 weeks. The last 2-3 weeks he has discovered his hands and has since been chewing on them his pacifier his bibs everything. Just yesterday he stared just with his thumb in his mouth. It looks like he’s trying to sooth his gums because it’s more chewing that sucking. He’s grabbing but not really holding on to things just yet. I’ve trying teething rings but he can’t really hold on to them just yet. Any tips on how to nip that in the bud?? I really don’t want him to start thumb sucking!