My eye started to itch last night and won't stop I used the Benadryl (diphenhydramine) pen after 3 hrs of itching when I got home and took Benadryl (diphenhydramine) and no help?

Probably allergic. It is most likely allergic conjunctivitis. Anti histamine eye drops work the best. There are a number of them available over the counter such as Opcon-A. If the itching continues, you may require additional medicated eye drops that include steroids. Consult your doctor.