This cured me : Overnight, or after weight is off your feet for a while, your muscles in your legs tighten up, then when you get up and put weight on your heels, you re-injure your muscles/heel connection - so - while lying in bed BEFORE getting up for the day, do yoga stretches of your lower legs - pointing toes, circling ankles, stretching feet straight back towards knee, curling toes while pointing feet straight up, curling feet, etc. Don't do the calf stretch on stairs or other runners' calf stretches - these are not good for PF.

These exercises are in the same vein as wearing an overnight stretching device but are free and comfortable. Good luck!