Pressure behind left eye for months. recently severe headache and dizziness, vision changes. eyes checked and ok. what could be wrong?

Hemicrania Continua: Hemicrania continua is a rare continuous one-sided headache that never shifts sides. The typical presentation is a dull throbbing ache that is moderate to severe in intensity. the primary area of pain is located in the ocular temporal region. They are also classified as an indomethacin-responsive headache disorder. See an orofacial pain or headache specialist for evaluation.