What Causes Large Red Painful Knot On Chest, Near Underarm, Stomach?

My husband is getting what starts out looking like an insect but, that turns into a large red painful knot. He had a couple a couple of months ago, the Dr thought it was either spider or Staph. Staph showed negative. He has continued to get these, mostly on his chest near his under arm. There are numerous spots now, one on his leg, on his stomach and chest area. He had to have the one on his chest drained a couple of months ago and went through a cycle of antibiotics. I am not getting these, so I am not inclined to think they are bites. Any ideas?