I Am Taking Clarithamycin For A Infected Cyst On My

I am taking clarithamycin for a infected cyst on my back. My last day with this medication is tomorrow and that finishes the 1 weeks prescription yet the cyst is still red raw and hasn't gone down.
I have a really bad cold wityh a chesty cough and wonder if this is interfering with the antibiotics. Booth the cough and cyst are really bad. What should I do?