What Causes A Sore Lump In The Groin Area?

This is not the first time, but I have a lump in the groin area along my underwear line. I had one removed about 5 years ago and since then I would get one every so often but it would be small. About a month ago I got 4 along the same side that were very inflated, painful, and uncomfortable to sit and move different ways. I was put on a medication that my doctor claimed would heal to "skin infection", but now again I have in the same spot a very enlarged sore lump. Any ideas?