Severe foot/ankle pain?

Back in April, I had an accident where I sliced open the top of my foot. I got stitches, and everything seemed okay. Within a few days of getting the stitches, the wound got infected with staph and it turned into cellulitis. Since then, I have been hospitalized twice for this and given antibiotics so often I'm likely immune to them all by now. The infection has cleared up, but here's the problem. Once the swelling goes down, it only stays that way for a week or so. I'm able to work without pain (I'm a chef) and things are great. Out of the blue, my ankle will begin to swell up on its own, with no new injury other than being on my feet at work. The doctors have done x-rays, MRI's, sonograms, and a few other things to determine what is wrong, but all tell me it is just in my head. I find this unnacceptable since my ankle looks like a grapefruit and is nearly impossible to walk on when it swells up. I should note that I do have flat feet, and have never really had much trouble with them until recently. Ever since April when the initial accident occurred, my ankle has had a mind of its own, swelling up and running its course for a week or more before I'm able to stand/walk pain-free. I have tried looking up different things to try pinpointing a cause but come up short. Any help with this would be great since it is really starting to get on my nerves.