There are such things as bed sores. Do you stay in bed a lot? I suggest going to the doc. as soon as you can .
You don't say how long you've had this spot on your leg. Is it possible that you've been bitten by a brown spider? Their spit causes the skin to die and fall off and causes a crater to form in the skin. - If it isn't a bite, did you get a splinter in there? That would itch like crazy.
If it's a brown spider bite, put a wet piece of gauze with salt on it to draw out the poison.
If it's a splinter, use a small piece of bread dipped in milk and sugar and tie it on the area with a rag. It should draw out the splinter.
Since we don't know what caused it, you might have to see a doctor to determine what it is.