Hi. I Had A Tiny Bump On My Arm Same

Hi. I had a tiny bump on my arm same color as my brown skin. It itched a little the first day but was no concern. Within 24 hrs it was clustered and filled with pus. It was the size of a cigarette end. The surrounding area was red and swollen. After a culture, it had no bacteria present. I was on a antibiotic which did not help. The skin came off and it was an open sore that was painful a itchy. It left a deep scar like a cigarette burn. 3 weeks later I have a new one forming about 2 inches away. Please help. I work in a hospital lab and I feel gross. I also have family I don't want to spend to. So far no one has gotten it.