I have a burning sensation in the back and bottom of my heel, where the back and bottom join. The burning is not constant. It gets worse as the day wears on and if pressure is put on the back of the heel - for example, sitting with feet on a foot stool. It is most noticeable and was first felt when I tried to do the downward dog yoga pose. I can flex my ankle and my hamstrings are very flexible. I can put my hands flat on the floor while standing with straight legs. I have started feeling it sometimes when my foot is flexed now, but this is a more recent development. I walk barefoot when at home, in the house, and this seems to be aggravating it now. Can you advise?