I've had a cough for about 3 days now pretty much none stop. I just coughed up blood. What does this mean?

See a doctor. Coughing up blood is not something to take lightly. It can mean a number of things, but you should seek medical attention right away so they can determine the cause.
Hemoptysis.... The most common cause of coughing blood, called hemoptysis, is bronchitis. However, this symptom always needs to be seen by a doctor because malignancy can also lead to hemoptysis. So, see your doctor asap. If you smoke, you need to quit today to decrease airway inflammation.