What could be the cause of swollen glands in my neck, fatigue, loss of appetite, headache, and itchy eyes?

Possible infection: Swollen glands are almost always a sign of infection. Fatigue, appetite loss, and headache are all non-specific symptoms that can also be related to infection. This should be evaluated by a physician.

Itchy: Causes of itchy eyes include allergy and blepharitis, an inflammation of the eyelid margin caused by certain bacteria. It is reasonable to try over-the-counter allergy drops such as zaditor (ketotifen). The swollen glands suggest infection of some sort-- discuss things with your primary doctor if you are not feeling better within 24-48 hours.