There are many reasons for a bloody nose including problems within the nose and sinuses. If you are having persistent problems, make an appointment to see an otolaryngologist who can help diagnose and treat your issues.
Bleeding from your nose is called epistaxis and can be caused by numerous things, including, small vessels on the septum, bleeding disorder, hypertension, nasal trauma from nose blowing or picking the nose, inhaled substances, allergies, sinus infections, polyps, cysts and many more. I would see an ENT specialist for a complete evaluation. If your epistaxis causes you to cough up blood clots, then understanding why your nose is bleeding and correcting the problem should help. However, if your nasal exam is normal and you are still coughing up blood (hemoptysis), then you will require a complete physical and pulmonary evaluation asap to find out the cause. Hope this reply helps.