I'm having extreme pulsating pain behind my eyes. what could this be?

See an eye doctor: Pain in or around the eyes that is excruciating, includes vision loss, and/or does not resolve on its own within a matter of minutes, should be evaluated by an eye doctor. The cause may be as simple as a migraine or atypical muscle headache, but can be related to inflammatory and other conditions. See an eye doctor as soon as possible.