From your description, sounds as though you may have what's called sebaceous cyst. With it being painless, it generally best to leave it alone, as it may just go back down. If it does continue to get larger or becomes painful. Then you can try to apply a hot compress or soaking in the tub with epsom salt. If that doesn't help any. Then you need to follow up with your doctor, as he may prescribe steroids or antibiotics. It may also need to be lanced as well.
You can read more about them here as well. read here
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