I had a "bump" taken off my back, not looking for skin cancer , and it hurt before I had it removed. The best description I can think of is it is kind of like when you pull a weed out of the ground there is still some left. Well it has been around 6 weeks since I had this taken off, path reports say fibrous cyst, and it hurts just like before. It too wasn't stitched and it healed nicely. Now I need to call dErmatology and ask why it still hurts.
The foot of course is probably harder to keep clean so it very well could be infected. I would definetely go back to have it checked out. It could also just be that a foot takes a lot more wear and tear than say a back or even arm and it just takes longer.
Good Luck!
B