How to stop bitting

I have a rat, he’s been with me since September. He wasn’t a biter to start with, but I’ve noticed since the start of this month he’ll walk up to me and start bitting me. I’m not sure if it’s his way of saying let’s play but the bitting isn’t just a nibble anymore, he is drawing blood and I don’t know what to do. He only bites when he’s out of his cage.I obviously yelp at him when he bites so he knows it hurts but I want to know what I can do to stop this behavior