This is kind icky but I used to have my nipples pierced and although I took them out almost 5 years ago the holes sometimes have white pus in them. I asked the doctor what was going on and he said that our bodies produce this discharge where ever there is holes (either man-made or pores). According to him it's kind of like a pimple but with less redness/inflamation and expelling the icky stuff gently along with washing thoroughly is ok.
coulda been an ingrown hair, I have had this before. keep checking it, if it is one and it doesnt go away then the hair is still coiled inside undder the skin. You can always check with a Dr. too. good luck!
Did the lump go away when you popped it?? It could be a hair bump. This happens sometimes. I have had this happen and it usually goes away in a day or two. However it is does not go away or gets worse, I would check with your doctor or nurse.