In reply to thelostjockey:
Get it diagnosed, could well be PF.. but could be something else and then all this advice may be wrong and make it worse
When I had PF (in my case more towards the toes, I thought I'd broken a metatarsal, the pain was terrible and hit me one morning when I got out of bed, no prior warning) my GP told me to stretch the entire posterior chain not just calves, although calves received more focus. Get a plastic 500ml Coca-Cola bottle in that classic curvy coke bottle shape. 3/4 fill with water and freeze it. Put it on floor stand on it to use as a roller under that foot, it may be uncomfortable treatment! (Put a tea towel over it).
Stretch calves and foot and hamstrings and lower back. When you stretch calves do it normally with a straight knee and also stretch calves with a partly bent knee, no idea why both but my GP was insistent and said both was needed.
Get well soon