Puffed up newborn lips

My baby is 3 weeks old and the past 2 days I've noticed when he starts sucking on the nipple of the bottle his lips start to get puffy and start looking like blisters. Could this be because he's sucking too hard on the nipple? Or allergic to the nipple? He's been using the same nipples since he was 3 days old and it's just now doing this. It goes away as soon as he stops drinking from the bottle.