Eating preservatives in food cause me severe migraines, why will no medication prescribed or otherwise take this pain away?

Allergy. You have food allergies. Get tested and the results will help you get better. The meds are not effective in this situation.
Fueling the fire. It becomes extremely difficult to put out a fire, when someone is adding fuel to it. The inciting stimulus must be eliminated entirely, if possible, to achieve best results. Otherwise expect suboptimal relief from treatment, even by methods previously effective.