Plugged duct or mastitis!?

Gah! I woke up yesterday and my right breast was sore - I assumed from being overfill, so nursed baby on that side first. It was still sore afterwards and continued to be sore the rest of the day - kinda felt like I had bruised it in one area somehow. Well, now I just woke up with a low-grade fever (99.9), googled, and am pretty sure I have either a plugged duct or mastitis.

Gah!!! I *just* went back to work last week and really don’t want to call out for any reason, but am also worried about this escalating if I don’t take care of it ASAP. My sister got mastitis and lost her milk supply entirely as a result. I really don’t want that to happen...