Thank you, thank you, everyone.
Woke up this morning feeling like I got run over by a train, breast still splotchy, red, and sore. Not surprising given the list of things that can cause mastitis that I found on kellymom -- I think I've hit most of them in the past few days! Wore a too small bra for a day between laundry loads, both kiddos are teething and that's thrown both latches and nursing patterns off kilter, have chronic oversupply, been super busy and not eating as well or staying hydrated as much as normal . . .

My bad.
Staying in bed this morning, drinking lots of water, doing hot compresses and cold packs, nursing as much as the kiddos will tolerate (dd thinks she's hit the jackpot!).

Hot shower and a garlicky lunch coming up as soon as MIL gets here. DH took one look at me this morning and gave her a call.

Thank you again for the advice; it's reeeeally appreciated.