Blood in mucus, chest burning sensation also present?

See a doctor: You may have a respiratory infection or even pneumonia. You need a chest xray to rule out a lung problem especially if you smoke. Your doctor can diagnose your problem as well as treat it.

Could be from: Either a viral or bacterial infection involving the upper airways like a bronchitis or even including the lower airways, like you see with pneumonia. I would strongly encourage you to see a doctor for a formal evaluation, as otherwise it's hard to more specifically diagnose you without a more detailed evaluation. Best of luck.

Difficult to say: The possibilities are broad and depend on where exactly the blood is coming from. You may have GERD or what is commonly known as heartburn. Bronchitis is another possibility in the right setting.

It varies.: It is not unusual to have small specks of blood in sputum (mucus) but the more blood the more significant the problem. It could come from trauma from forceful coughing. The strain from persistent coughing can be painful, even in trivial conditions. However, If there is fever together with chest wall pain when breathing you may want to see a doctor to rule out pneumonia.