In the morning, while still in bed, my sister had difficulty getting a full breath. She had difficulty two days earlier after taking a short walk. She said she had difficulty getting a full deep breath. She has never had this happen before. She is 64. She began taking an antibiotic for an infected cyst on her back on Mon. evening. She doesn t have any other symptoms. What is causing this? Is it A reaction to the antibiotic? She is allergic to penicillin and is taking a different antibiotic.. Or is it some other cause?