My migraine caused a nose bleed from the back of my nose two days ago and lately I have been tasting blood in mouth but I cannot see it in my mouth.?

See a dentist. Blood in saliva can be a sign that you are at risk for, or already have, gum disease. Untreated gingivitis can lead to the tooth loss and other health problems. See your dentist ASAP because the sooner you treat it the better the outcome.