What Causes Lump On Foot Leading To Swelling Of Toes And Knee?

The top of my foot has been hurting, sometimes badly, for about 3-4 months. Eventually a lump developed in the area where the pain started. Now I have swelling into my toes, my foot and up my leg to my knee. There is redness that is easily visible traveling up my leg from the lump. It is a definite line. My foot feels constantly like it is being compressed, like in a compression stocking. I was sent for a Doppler that was negative for DVT and put on an antibiotic. There has been no improvement. Any suggestions?