Hello everyone! Girls, who have babies sucking their thumb, it's okay …

Hello everyone! Girls, who have babies sucking their thumb, it's okay with fingers, knuckles are fine, gums itch, but I noticed when he sleeps and it's time to feed him, his thumb in his mouth and then lies down, he deceives himself. How to stop it? They say this is a bad habit to suck on your thumb and affects the bite, we're almost four months old.