Re: swollen foot from skin biopsy
You don't say specifically what kind of biopsy was done in the area. Did you have a simple topical skin biopsy? (mole removal) Or have you had something more extreme, such as a sentinal node biopsy? A mole removal, where the biopsy comes back negative, should not result in any swelling that I'm aware of. Especially 3 or more weeks after the procedure.
With the absence of heart problems or diabetes or medication, the only thing I might think of is some sort of water retention. But then, you would have the condition in both feet normally, not just one.
As far as a doctor to see, you might want to call the doctor who did the biopsy. (I'm not sure if that was a dermatologist or your primary care physician?) Perhaps you could tell them over the phone what is going on, and if they feel they need to see you, you can go in. They may refer you elsewhere.
This is a bit strange, but I'm sure there is something very easy to remedy at the heart of it.