Blood comes out of my left nostril all of a sudden if i try to blow my blocked nose 3-4 times a month please advice as not been able find any allergie

Blocked nose: Not allergy related need evaluation from an ear, nose , throat specialist to check for polyps or any other growth. It could be trauma to your nose years back causing septal deviation now affecting how you breathe . Nosebleeding is from you blowing so hard on your nose.Need blood test if you have easy fatigability, easy bruising, etc to rule out blood disorders

Nasal Lesion: It is hard to tell what the cause may be. However, since this is a chronic problem and occurring on one side only (or mostly), see an otolaryngologist (ENT) immediately for a more complete examination.