Firstly, get your cat spayed. Unplanned litters end up in dreadful places.
Secondly, three days after birth, your cat should not be "bleeding". Discharge is normal for about 48 hours, and maybe some light spotting up to five days following, but if your cat is actually producing blood (bright red or dark red) something could be wrong such as an infection, retained placenta, etc. Ideally, the cat would have gone to the vet within 24 hours of the birth of the last kitten so that she could be assessed.
Keep an eye on her and don't panic just yet. If she continues to bleed past day five, the vet is a must. If she seems lethargic, loses interest in her litter, has a green or foul smelling discharge coming from her vulva, runs a fever, stops eating or drinking, or just seems "off", you should get to the vet immediately.
Again, don't panic as it is probably perfectly normal, but remain vigilant.