I think it's only around 2-3months that they start sucking their hands to self-soothe, before that it's more likely to be a hunger cue (which can still happen while they sleep) - what's his feeding like? Is he gaining weight well?
Feeding really well and putting on about 1 pound a week. Probably comfort as he loves a comfort feed!
Is it a hunger cue ? Or needs comfort? Good to question the need first before bringing dummy into it