It does sound like you might be developing PF. That sucks, but it often responds well to aggressive self-treatment.
A few things…
Go to a good running specialty store and get fit for shoes. This is critical. They can probably also hook you up with the Superfeet insoles mentioned previously, they can really help if you have flexible feet that over-pronate.
Plantar generally affects two types of feet more drastically…the very flexible ones that stress the fascia by over-flexing and the very stiff ones that are stressed due to impact and concussion. Both situations produce micro-tears in the fascia at a rate faster than the body can repair.
An accomplished shoe fitter can help get you in the right shoe/insole combination.
Icing, use of anti-inflammatories, massage and some simple exercises can also help. Committing to a 2 week “course of treatment” can work wonders.
Ice several times a day for 10-20 minutes if possible. After doing gentle stretching and exercises is best.
Exercises to strengthen the intrinsic muscles of the foot, and take some of the burden off of the plantar fascia, are simple and often very effective. Putting a small hand towel under your toes and then “scrunching” it up under your foot and then pushing it back out is one. Use your toes to pick up marbles or pencils or whatever. Both are easy to do and won’t take much time.
Cross fiber massage from the heel to the forefoot is great if you can find someone to do it…chances are slim that you can do it forcefully enough to your own foot. It just hurts too much. A frozen water bottle can massage and ice at the same time.
A golf ball is often mentioned, but for $7, the Foot Rubz ball is a bargain. It has projections that increase it’s effectiveness.
Stretch out your feet before standing first thing in the morning. And wear shoes for that first, and all subsequent steps.
Plantar can be debilitatingly painful, but if you get on it and treat it consistently you can nip it in the bud.
Good luck!
G