Even if you can get back to your old self, it will take some time, be patient and keep slowly increasing your activity. As for this coming on all of the sudden, that's how my PF happened, one day the foot just 'went'. I was a chronic abuser, ran around barefoot on concrete, wore pretty shoes that made my toes and feet hurt but so what, I got away with it for a long time. Then one day the heel hurt and it didn't go away, nothing to pin it on, nothing different, it just had had enough.
If you don't improve, go back and ask for another opinion, push the doctor if you have to, and let us know how it goes.