Uhh... yeah I would take your dog to the vet...
You need to at least call a veterinarian and ask them if they think your dog needs to be seen by them.
yes they do, all dogs do when they're in heat
Yes. Females do bleed when they are in heat. I would suggest keeping them in a linoleumed or tiled area to make cleaning up after your pet easier. You can also purchase "doggy diapers" for this specific purpose.
no but it is disgusting!
A dog's anus may turn black due to pigmentation changes, skin irritation, or underlying health issues.
My dog doesn't.
It is recommended to consult a veterinarian for a proper examination and diagnosis of any unusual spots or markings on your dog's body, including the anus.
Mucus
If your dog is throwing up mucus and foaming from the mouth they may have eaten something poisonous. You should take your dog to get medical attention as soon as possible.
Yes, fleas can infect a dog's anus. It is not uncommon for fleas to be found in various parts of a dog's body, including the anus. It's important to thoroughly treat the dog for fleas to prevent reinfestation.
You bleed.
Some dogs will go back into heat soon after having puppies, even if they are still nursing them. In that case, it is normal for a dog to start to bleed after 4 weeks of having puppies. If the blood smells bad, looks odd, or if your dog seems ill, call your vet since she could be in need of treatment for an infection or other problem.