When I do crunches, I get terrible eye pressure. Is this normal?

No. Sometimes valsalva maneuvers can increase eye pressure. Patients with pigmentary dispersion syndrome may have increased pressure during exercise. Best to have your eyes looked at by an eye care provider.
It shouldn't hurt. Although eye pressure can go up when we strain (bearing down, hand/head stands), the pressure should not get to a point where it causes pain. Does your vision change as well? I recommend that you have your eye pressure checked and have a dilated eye examination by an eye doctor. You may be getting a greater-than-normal elevation of eye pressure, which should be evaluated.