What Causes A Painful Lump In Groin?

Hi I have a pea size bump in the groin of my leg with irritation. It is very sore and swollen. I have had a virus, bronchitis, and sinus infection for 4 weeks. I have had one round of Bactrum 800 mg. twice per day for 10 days. As a followup to Bactrum, I was put on Augmentin 875 mg. twice per day for 10 days. I am wondering what this sore bump and rash could be. Any ideas?