I bit my lip in my sleep and it bled a little. Now there's a lump that resembles a blister but isn't painful and has no pus. What could it be?

Mucocele. Sometimes trauma to the oral mucosa can cause you a small cyst like structure underneath. If it is small and not bothersome, continue to observe it. If it grows or causes discomfort, see an ent.
A blood blister. A small amount of blood bled into the outer layer of the tongue causing a blister. As long as their is no pain nor pus, it will resolve within a few days.