whenever i sneeze i see blood in spit. is that because my nose is blocked due to allergy?

whenever i sneeze i see blood on spit . I don't cough blood at all. I dont know if it is due to allergy coz my nose is blocked often. But i never have blood coming from nose.I do have gum problem but i see blood coming from gums . But i don't know where is this blood coming when i sneeze . I used to smoke cig before. Anyone .. help