Good luck with the feet....but did talk to your doctor about the cause.
I know the first onset of pain was just after riding in the heat for an extended period but plantar fascitis is generally the result of overuse activities and poor arch support. Neither of which would occur while riding unless you were standing on your pegs a lot of the time.
Hope things get better quickly for you.
'12 H-D Road Glide Custom
'09 Suzuki DR650
'09 H-D XR1200