When it comes to your breasts, I'd highly recommend not waiting to call your OB/GYN to see what they recommend.
I had what was initially diagnosed as mastitis. They brought me in immediately, gave me a thorough exam, sent me for an ultrasound, etc. They did the same thing a few weeks later when I wasn't better. It ended-up being something serious but not related to my breasts.
Chances are, it is just mastitis or a blocked duct, but none of us can make that diagnosis, and my experiences are that your doctor would rather see you and be sure than have you diagnose/treat yourself with breast related issues.
Good luck!