Been having a burning sensation in the middle of my chest all day. i don't have acid reflux ... what is it?

Several thoughts: Burning sensation in the middle of the chest is often due to esophagitis(inflammation of the esophagus) from acid reflux in a 25 year old patient. Not unusual to experience esophagitis even though you don't notice reflux. Inflammation where a rib attaches to breast bone is called costochondritis. There will usually be tenderness to right or left o;f the breastbone.