knots in armpits

Over the past month I have had several pea size knots in my armpits. Several weeks agi I had one that went away on its ownin less than a week.2 weeks ago I had three come up at one time in the same armpit.2 of these eventually became swollen(so much so I could barely lift my arm at all) and irritated and one came to a head with pus and blood drainage.Just last night I had another one come up in the same armpit.It is tender to the touch, but not so much I can't touch it.I have also had several places come up on my face that are hard to the touch, but eventually look like just a pimple or blackhead even though nothing comes out of them. Then they fade away within 6-8 days.What could be causing these?