This is usually a sign of infection. You could have a clogged duct or a yeast infection has been transfered from the baby's mouth to your breast. It could also be an abscess in your breast which can be a serious condition. This is something that should be discussed with your doctor.
If red puss filled the pump on your breast then you should not breast feed a baby. Dispose of any breast milk and contact your doctor. There might be an infection and you do not want to pass that on to a baby. To avoid being engorged, you may continue to pump then dump the milk.
You need to call your doctor and explain exactly what has happened. It sounds like you have an infection in your breast. I would do this asap because you should not feed the baby until you know what the cause is. It may be something you could pass on to him/her.