Swollen, sore left eyelid causing a headache on the left side. no redness of the eye and vision is not affected. what otc medication can i use to reduce the inflammation and pain?

Sounds like: "Blepharitis" an infection of the eyelid! This usually requires an antibiotic locally (sometimes systemically) (thus requires an in person visit to an eye professional. However sometimes soaking your eye in an eyecup (common pharmacy item) three to four times per day for five minutes at a time with plain pure warm water may relieve the discomfort Hope this is helpful Dr Z