I got a bout of plantar fasciitis from wearing a size to small shoe last summer.
They fit fine when I bought them but it was early in the day so my feet hadn't expanded or swelled as most feet tend to do by afternoon time.

When we had a heat wave I noticed then after a few hours I had to take them off - they just got tight overall.
I had no clue this might cause something like plantar fasciitis...

I finally asked my chiro about it and he mentioned arch support/orthotics and the stretches... but he also did some ultrasound and low level laser tx on my heel and foot.
Just needed it the 2 times so far and with orthotics in my shoes- and got rid of the too small shoes -and make sure now to get shoes that are roomy.
Now I only notice it a bit if I hold my foot in a odd angle and then walk right away.

You may have more going on than I did, but the low level laser is supposed to help with all kinds of healing and painful areas.
Also called cold laser.
http://www.laser.nu/