My dogs are bleeding help !?

ok my dog has had a phantom pregancy (again) but this time theres blood coming out of her nipple but only out of one of them normaly blood dont come out a little worried as you can probly understand also shes about 8 years old ermm she hasnt been biting or anything like that and yes i no to take her to a vets witch i will do asap id just like to see if anyone could tell me whats wrong thank you all :)