Are there over-the-counter medications that help treating covid-19 and reducing its severity?

Maybe: There is some evidence to suggest that Vitamin C, Vitamin D, melatonin, zinc and Quercitin MAY be helpful in prevention in older patients. This has not been proven.

Medications: There are no cures. If you have mild disease, consider having a decongestant, acetaminophen or nasal saline irrigant in your home. There is no current evidence that supplements will protect you from getting the disease. If you are deficient in any particular vitamin - consider supplementation (Vit D. Vit C, Zinc, B complex)