Shortness of breath with minimal exertion activities, not a problem when exercising. Suffer from migraines and GERD. Early 20's and otherwise healthy.

Graduated exertion. If shortness of breath is due to a pathologic process (aka "disease"), it progressively worsens with increasing severity of exercise. If I understand you, you become breathless early on but, when you exercise more, it gets better or at least doesn't interfere (?) - to me, that suggests a "warm-up" phenomenon. This is physiologic, not pathologic (aka "normal). Increasing fitness should alleviate it.