Cramps in the arch of my foot

Whenever I do lunges I get this horrible cramp in the arch of my foot. Sometimes it's bearable but other times it's so bad I have to stop and let it rest or massage it.

I heard from some people on this site to use a tennis ball or golf ball and roll it around on my arch to stretch it out. I keep a golf ball at work so when I'm at my desk I can take off my shoes and roll it.

I did this yesterday at work and it felt good. When I did lunges this morning I actually didn't cramp up. I stuck out an entire set of lunges without freaking out.

However just now I went to roll the golf ball and my arches are sore. Why is that?

I've been told that it's all about the shoe. I've gone to the shoe store, told the guy what was going on and he suggested a few types. I tried them on, walked around, did some lunges...but you don't really know how it'll work out until you're using them at home a few times. Needless to say the pair I have now isn't really doing the trick.

Is there a sneaker that is better than the other?

How often should I be doing this golf ball exercise? Daily? More than once a day? And is it normal to be sore like this?

Any info is appreciated!