A bubble inside your navel, abdominal pain, could this be a hernia?

Yes: Umbilical hernias appear as bulges at or slightly above-or-below the navel. They can yo-yo in and out or can become "incarcerated" with fat, and protrude constantly. Many people have no pain yet it is possible to experience some discomfort at the bulge, often worsened by activity. The best test to diagnose a hernia is to undergo a physical exam by a hernia surgeon; your primary care dr. Can triage.

Yes: Yes, it could be. Imaging through an ultrasound or ct would provide an answer. A physical exam by a physician would help shed light as well.

Possibly: A bulge or bubble at the navel is often due to a hernia. When pain is present, this should be examined by a physician as you may have intestine stuck in a hernia defect. If so, this can result in blockage or rupture of the intestine.