I hope that it isn't mastitis for you. Could you be a little engorged? Did bub sleep longer than normal last night? I had mastitis in hospital and again it started this week. But this time I managed to get on top of it at first signs. When I was in hospital they put me straight on anti biotics and I got physio using ultrasound everday. If it persists You should see the doctor. Don't let it linger in hope it will get better. In the mean time though, hot packs on breast before feeding, massage and feed it out. The physio told me to massage with the back of an electric toothbrush. Also take panadol to keep temperature down (another sign of mastitis).

Good Luck, take care and look after yourself