Rabbits DO NOT have periods. They do not have an estrius cycle like most mammals, they are what are called enduced ovulaotors. They only ovulate once they've been mounted by a male and the act of sex triggers the female to release her eggs.
If you have a rabbit that is bleeding from their genitals, and you are positive it is not red/orange urine, then it is a serious problem. It can be a sign of bladder/kidney infections or worse it is also a sign of uturing cancer/infections.
If it's a pregnant female that's bleeding, then she's having serious problems delivering and needs a vet immediatly.
So, if you have a rabbit that is bleeding from the genitals, it is a serious situation. The rabbit needs to see a vet as soom as possible.
Carolyn84, if you are finding blood, then take her to the vet. Chances are it's either an infection or uturine cancer.
Hollybunny: If you rabbit is also bleeding from her genitals, please take her to a vets because it is not normal. She is probably grumpy from not being spayed and being full of hormones, not from getting her "period".
--Dawn