Is it on your eyelid? (Kinda where females would put eyeliner). If yes then likely a chalazion. It is caused by blockage of a gland. It will go away on its own. But you can try a warm wash cloth to help speed along the process. If doesn’t go away within a couple of weeks I recommend going to see your doctor.
It's probably a stye and it has grown in size because of pus accumulation. It is supposed to go away on its own, think of it as a skin pimple but just in the eye. I agree with Sports1022 concerning the advice.