Your best bet is to call the doctor who has prescribed this antibiotic to ask if your skin reaction is a possible side effect to the medication or whether the antibiotic did not work for whatever reason. There is no way we can tell you what has caused this reaction.
What kind of antibiotic did you use? If you give us more information perhaps we can research this for you. But the best advice I can give is to call your doctor or even your pharmacist.
Thank you for your question.