You get a very specific localised pain in one boob, with the inflamed area become steadily larger and more tender. The aches and shivers are secondary to the agonising pain in the boob.
I didn't have a red patch particularly (had 5 or 6 bouts of mastitis with dd2) but definitely localised pain starting as tenderness and mutating rapidly into agony.
Generalised soreness in both breasts doesn't sound like mastitis, tbh. There is a nasty sore-throaty fluey bug going round atm.