C.M.
sounds like a clogged duct which can develop into mastitis if it doesn't clear out. If you start running a fever and achy flu-like symptoms then it's time to call the Dr. (i've had it twice with breastfeeding 3 kids each for a year)
I would pump that breast for at least 15 min every 2-3 hours. Massaging the hard spot with my knuckle while pumping. Massage in circles and push toward the nipple. A warm compress before pumping helps too. I was able to relieve my hotspots within a day if I was diligent.