You, my friend, have what methinks to be the LOW-CARB FLU. Eek!
What you have sounds like allergic rhinitis - hay fever. Being three weeks into the PB, however, I suspect that you're just experiencing the effects of going off the bad carbs. We all experience it a little differently. Take it easy on yourself, seek comfort, and stay on track. It's your best bet. I'll be over in a week or so.
EDIT: or do you mean to say your three weeks into the mucus-fest? IF that's what you mean, oopsie, and I flip-glop back to hay-fever. It's early spring in Ontario, right? Have you tried something for hayfever? I myself, am having a horrible hay fever season, the worst in many years.