Unfortunately, bharat has the most likely diagnosis - plantar fasciitis. Of course, only an exam by a doctor, or in this case a podiatrist, can tell for sure what you have and what to do. But you may still find the following information helpful.
The plantar fascia is a long flat band of "connective tissue" (that behaves like flexible plastic) and connects the "heel bone"
to the bones that make up the "ball of the foot".
Thus the plantar fascia forms the base of an arch, with the roof of the arch being made up of the bones in your foot.
The plantar fascia normally keeps the arch from being able to fully flatten out when we walk or run.
But that means the plantar fascia is "stretched" each time we take a step.
The result of all that "stretching" can result in the inflammatory condition known as plantar fasciitis.
The best way of treating it consists of rest and support of the overlying arch.
Rest is needed for the inflammation to subside. That means no tennis and minimising the amount of walking done.
Support means providing a shoe insert that will push up on your arch so that the underlying plantar fascia is not being "stretched" so much.
SystemicAnomaly has been good enough to report that the Dr. Scholl's Custom Fit Orthotic Insoles available at kiosks in many pharmacies have been helpful to him and appear to provide a good way to find the right size orthotic/insole:
http://tt.tennis-warehouse.com/showthread.php?t=338089
I have a fairly high arch, and like the Superfeet Orange insoles, but as you can see at this site, there are a lot of different insoles out there:
http://www.runningwarehouse.com/catpage-insoles.html
Of course, the absolute best fit is from a podiatrist who can make a specific recommendation, and even make custom orthotics.
The insole or orthotic is probably more important than your shoe or tennis shoe, but obviously some shoes may be better for you than others.
And certainly what you don't want to do is let this become a well-engrained inflammatory condition that tortures you for many months like it has for too many who have posted here about their difficulties with this malady. So give your feet that rest and get after treating this problem.
Good luck!
