Burning on the bottom of my feet

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I purchased a pair of basic Asics after the birth of my son in the fall. I wore those shoes to get back into shape. A couple weeks ago, the bottoms of feet started to burn when I ran. So I thought it was because I had cashed those shoes and needed a new pair. I went to the running store and purchased pair of Asics 2140s. I have gone on 4 runs with these shoes (average 5-6 miles) and the burning sensation has not gone away. I have never worn the 2140. I usually wear the Kayano, but I didn't feel like spending the money. Is there something going on with my feet or am I just in the wrong pair of running shoes? I am wearing cotton socks, but that is what I have always worn and even running longer distances, I have never had a problem. I am getting concerned because I signed up for a marathon and I am about to begin my training program in a couple weeks.
I am a 33 yr old female. I weigh 130lbs and I am 5'5" tall. I live in the upper Midwest.
Also, the burning is only when I run.
Thank you!