Won't stop nursing 😭

My baby is almost 3 weeks old, and I have been nursing him for 3 hours now and he'll unlatch himself but then acts hungry still right after and will start crying until I feed him again. I've tried giving him a soother and he won't take that. I know he's probably going through a growth spurt, but how do you tell if they're actually hungry or just comfort nursing? My nipples feel numb from the constant nursing and I don't know what to do!