It's probably a staph infection, I had that in both pits for about 9 months in total. Started as a lump in my right armpit which got christened Rupert, just as that exploded statisfatorily all over the shower cubicle at an unnamed backpackers I got two more in the other armpit, they were called Lachlan and Elizabeth (children of Rupert), they went with antibiotics, then I got another Rupert and so it went on. I had about 5 months of tablets, a number of breast checks and a diabetes test before returning to Britain and being told by my doctor that I was having no more antibiotics and they would go away of their own accord. They did eventually.
Anyway, main advice I got was keep it all clean, wear natural fabrics, don't use anti-perspirant (that one got ignored a few times) and don't shave.
As an aside mine never showed up as red pussey lumps, they were just lumps until they exploded, when they became a mess.