I have bronchitis, I'm taking doxycycline and benzonatate do they cause blood to be in your bowel movement.?

Blood in stool. If there is diarrhea with blood, it's urgent that you get tested for c. Diff - possible superinfection from antibiotic use. If so please see your physician again.
Unlikely. Unlikely cause bleeding , unless have other etiology , this is to be taken seriously and to be advised by gastroenterologist .