Shellstar

Try to have a look at it. If it is red or white and you can see an obvious pimple type lump then it is a sebaceous cyst.
You can help to get rid of this by washing the area with very hot water and soap. You could also try to exfoliate.
If you can not see much apart from maybe a bump under the skin then it is a swollen gland.
Ngala is correct this is usually caused by an infection of some sort and should go down on its own.