Do you shave under your arms? Could be ingrown hairs. Rub salt mixed with a tiny bit of water under your pits if its ingrown hair it will stop the pain and about 2 days gone.
My friend had the same thing happen to her it took a few weeks but it went away
Depending on where at in ur arm pits it could be clogged milk ducts or you could be gorged since you quit breast feeding and pumping. I use to get clogged milked ducts all the time. Somtimes I had to put warm compresses on it and massage The bump then pump or breast feed. If ur pump broke you might be able to find a hand pump cheap or even hand express. If it doesn't go away I would go in to see u dr. It could be an infection that u have to take an antibiotic I know I had to do that.
For a second I read "under arm pit breast milk" LOL. But I agree with the ladies above