I'm not sure what you have either, but it MAY be plantar warts; they're pretty common, can be painful, often appear on the feet, and sometimes the hands. Plantar warts often have what looks like one (or more) tiny black seeds in the middle of the tough, thick bit of skin. Sometimes they're difficult to see.
If they're painful (and even if they're not), it might not be a bad idea to see a doctor or stop at the clinic. Once you know for sure what they are, there might be an inexpensive over-the-counter remedy for it.