Extreme pain bottom of foot

I developed suddenly a small bump (pea size) on the bottom of my foot just below my small toes on the right foot. My podiatrist dug it out. It seemed fine for 3 weeks, then another one grew. After three times, he took me to surgery. He removed a small mass - nothing came back on the biopsy. A month later the area of the incision is so sore I cannot walk on that foot - I kind of hobble - and putting my foot into a sneaker is REALLY sore. I have another appointment on Tuesday - but am concerned that no one seems to know why this keep recurring - and it is so painful. Nothing removes the pain. If I sit with my foot up, it isn't bad, but any kind of walking, and I do walk, makes you want to sit down and have a good cry. I cannot afford to keep going to the podiatrist.