Pain in balls of feet can be due to plantar fascists. Typical symptons are equisite pain in the ball of foot after resting.
Here are some exercises that help it. I've had it 3 times in my life as I was an avid walker. All the rest during chemo finally cured mine. Haha. But the exercises made recovery so much quicker than resting alone plus a heel pad...lots on the market. If you google you will understand how it happens.
http://footlogics-shop.com.au/page/28/Plantar-Fasciitis-exercisesIf no improvement hsve a tefferal to a physio as sonetimes a splint is needed.