I Was Taking Cephalexin For An Infection On My Are

I was taking Cephalexin for an infection on my are from being scratched. 500 mg 3x per day for ten days. Around day 5 a rash started forming on my other arm. On day 6 I cut back to two pills. Day 7 I took two pills.
Did not take any more after that. Have been putting Aloe Vera, from a plant, on it and it looked better, but now it is getting worst. Itchie and very dry skin. I wash it with an organic soap 3-4 time a day. It is warm to the touch and is getting bigger.
Shirley