My DD started with such complaints in kindergarten at a terrible placement ending up in the nurse's office almost daily with a stomachache. I thought it was anxiety from a combo of terrible teachers/bullies/inappropriate work. Turned out that yes she had developed anxiety but also was VERY 2E with just about every imaginable learning disability AND was experiencing migraines. I found out after the fact that migraines in young children commonly manifest first in stomach pain known as abdominal migraines. It was fall of 1st grade that she started to present with the more traditional appearing migraine and we got a diagnosis. So yes it may be just boredom and stress but it could also be fluorescent lighting, loud group activities, visual noise (some patterns in clothing or on certain wall charts can trigger my migraines big time), smells, certain foods, etc.
