This really does depend on the amount. I personally was blessed that my sores didn't really open up. Though my throat was sore and tight. I used to cough up phlegm all the time ( I'm an awesome spitter now) but blood - no. If it's just a little it may be related to the sores and irritation, but I would still have it checked for peace of mind losing lots if blood is never good especially when you are already immune compromised.