Red painful feet

I had l4 l5 back surgery about a year ago. Three months after the surgery, I began to have painful heels. I went to a podiatrist and he said it was planter fasciitis and fitted me with orthopedics. I wore them for several months with no relief. He then tried prescription anti inflammatory meds. and cortisone and no relief. I then went back to my ortho doc. He thought it might be nerve related and sent me to a pain clinic. The pain clinic doc. has given me cortisone injections and sent me for an emg which came back negative. I still do not have an answer. I am in sales and am on my feet 8 to 10 hours daily. The bottoms and backs of my foot are bright red and my heals are very painful. I do not know here to go to get an answer. Any help would be greatly appreciated. the pain is worse sitting or standing for long periods of time. Also the backs and bottoms of my feet are red and a little swollen. Is it my feet or back or a combo of both. Sorry for rambling.