Dull pain in upper left anterior under rib cage with stabbing pains, gradually getting worse for a week, headache, fatigue, neg. Mono test?

Costochondritis. Costochondritis is inflammation of cartilage between the ribs and is associated with a viral illness, smoking, and other causes such as trauma to the area, physical activity straining the rib cage, arthritis and other causes. Try ice on area, ibruprofen/tylenol to relieve pain, avoid activity that makes it hurt. Check with doctor for to determine cause of pain. Physical therapy after doctor chkup.