It may be just a coincidence, but I recall having something like a pimple or an infected milk duct in my right nipple a long time ago, maybe 30 or 35 years (I'm 50). From then on I had a spot on my right nipple that appeared to be an extremely tiny hole (think sewing needle size). If I squeezed the nipple, a soft, white pulpy mass like you described would come out in a long, string-like shape that looked toothpaste being squeezed from a teeny, tiny tube. I always thought it was just natural body oils building up in my nipple somewhat like a blackhead would be caused by oils in my pores. I thought it didn't turn black like a blackhead because I wore a bra for so many hours a day, it was in a warm, moist area (especially during the summer) and didn't get a chance to dry out at the surface like a blackhead would. Also, when I was close to having my period, both breasts would be very tender and if I squeezed the either breast, a greenish-yellow watery substance would come out of the milk ducts. I would sometimes squeeze some of that out because it seemed to take the pressure off. I showed a couple of doctors, but they said it was unusal, but nothing bad because both breasts did the same thing. Last January I was DX with IDC in the right breast, with 2 tumors, the largest one being just above and almost directly aligned with the nipple. Please have your spot checked out. I wonder if my little bump was the beginning of cancer and I would like for you (or anyone else, for that matter) to discover yours much quicker than I did or prevent it altogether. Best of luck, kiddo.
Dear closet, Without being able to examine this, ask questions etc. it is impossible to say what this is. It is best to have it checked out by your doctor. You may want to start with your rheumatologist as it is possible that it is related to the lupus.