I Have A Chest Infection And Have Been Given Clarithromycin.

I have a chest infection and have been given clarithromycin. I have an allergy to penicillin and sometimes feel very strange when I take certain antibiotics. Metronidazole has given me a rash in the past.
So needless to say I get extremely anxious when I take antibiotics. I feel I need to for the chest infection and the the doctor also expects I have developed psoriasis(which has spread) as a result.
Any advice for keeping me calm to take this medicine and reassuranceI am not going to have a bad reacion?!