
It could be a wart…try some wart treatment which you can buy OTC. Using a corn plaster on it could be very useful to destroy it.
Or it may be a foreign body which has entered your skin…something like a splinter or piece of glass, or tiny fragment of metal. The bodys natural defences make a protective shield around it which is the lump. If this is the answer then you could have a minor op to remove it, only takes a minute or two.. I had a lump like this and had a rose thorn embedded in my knuckle but certainly dont remember when it entered the spot.
If the wart treatment doesnt work then go see your GP if you are in UK.