What Does A Bump In Armpit Indicate?

I had a bump in my armpit for years that would leak stinky pus when squeezed but never fully popped .. Recently I made a small incision and drained the puss and the hole was dark almost black.. I dug inside with a needle and a thick ball of hair came out it was like dime sized ball of hair .. I cleaned with alcohol and washed the area.. The swelling came down some but there is a small hole. Should I go to a dr and how did this happen in the first place