I Have A Red, Swelling On The Upper Eyelid That

I have a red, swelling on the upper eyelid that is sometimes painful. Look almost like a large pimple, but never comes to a head. It is just above the eyelashes, perhaps includes them. folliculitis mayber? This has been waxing and waning for a month or two now. I is not always sore, but it does look like it should be. How do I treat this?