You could be having a period. Your cycle can be very erratic during breastfeeding. While nursing my older two children I had no periods for 13 months each time. With my third, my period started back at 6 weeks. I could not believe it! I got pregnant when she was only four months old, and miscarried. After that my periods came back like clockwork. I'm 9 weeks postpartum with my fourth baby right now. I've already had some spotting a few weeks ago. Just so you know I breastfeed exclusively on demand. In my experience, nursing during a period is pretty miserable. I agree with Betty in regard to mastitis. I've had it several times. I use colloidal silver to treat the infection instead of antibiotics, which I never take. For swelling and pain, try placing cool cabbage leaves on your breast. Sounds crazy, but it really works. If you're concerned about pregnancy you could always get a cheap test. Good luck!