Yeah, gregf83 has it right. You didn't build enough of a base - 250 miles/month isn't that much - and then you doubled the mileage and increased the intensity at the same time. Inevitably, you are paying the penalty. You aren't giving your muscles time to recover from one hard effort before doing another, and that doesn't make you stronger, it just breaks you down.

Rest is best. Take a week off, now, to recover fully. Then follow greg's advice. You'll be fine.