What can be the cause of chronic nose bleeds. Normal BP. No sinus problems.

Trauma. Frequent nose bleeds can be from trauma. The nose has a tremendous blood supply. After the first nose bleed you may find additional nose bleeds hntil it finally heals.
Try to keep the area clean and moist but dont pick the scab or blow your nose too hard etc. try nasal spray to avoid the itching.
Some causes listed. Chronic nose bleeds mus have some basis- either inside your nose or due to a bleeding disorder.
You should go to an ENT doctor to check the inside of the nose as there can be a vascular malformation which can be corrected by the ENT doctor.
A medical doctor may be able to help in checking your blood for any bleeding/clotting defect which requires blood tests like platelet count, bleeding/clotting.