I felt really sick today, 2 days after finishing z-pack for brochitis?

thursday i went to the doctor because i felt sick. he told me i had a very small case of bronchitis but mostly allergies. He gave me the three day antibiotic called z-pack and cough medicine, it was going great now ive been off of it for a couple of days and i feel very tired, weak, cold, and like i havent eaten. this morning i was coughing up a storm (i never cough unless im really sick) i dont know whats going on.