I had some cajun fish, and afterward I had the warm feeling in my stomach, slight nausea. Could it be GERD, or migraine related? I had HA 1 1/2 days.

Stomach acid burns. Acidity can definitely cause a warm or even burning feeling after eating, as well as nausea, a cough, feeling of something caught in your throat. (worse with citrus, fatty foods, alcohol and more). if you notice this feeling with food, likely not migraine related. migraine related nausea occurs with migraine. uncontrolled acid may lead to ulcer; doctor can prescribe for same.
Sounds like. you and Cajun spices are not "meant to be"!!!! Both gastric and Vascular (migraine) reactions to this usually delightful spice combination are quite common! Avoidance (or smaller portions) may be the answer! Hope this helps! Dr Z.