As much as I hate going to the doctor, a podiatrist might be the answer.
Though, if it were me, I'd probably throw some salicylic acid at it and cover it with a bandaid for a few days to a week, then dig out whatever foreign object is in there with a sharp knife, be it splinter or the core of a plantar's wart (and those things to suck big time).
47 M 5'8"
May 4, 2010...... 440? lbs. (Start FitDay Size 60 Jeans)
June 19, 2010.... 393 lbs. (First Weigh-in)
June 19, 2011.... 229 lbs. (164 lbs. gone in one year :-)
Current Weight... 185 lbs. (Size 36 Jeans)
Next Goal 169 lbs. (07/04/12)
Ultimate Goal 165 lbs. (12/31/12)
The best exercises for weight loss are Fork Putdowns and Table Pushaways.