Hi,
After going through your question, there are following possibilities for pain under rib cage
1) Pain related to heart associated with sweating,
palpitation, breathing difficulty with exertion (as in your case) .
2) Pain related to stomach (acidity) pain is burning in nature though there should be some relief after using antacid medicines.
3) Pain related to pancreas as in
pancreatitis usually pain is severe associated with
radiation to back.
Following investigations may help in making diagnosis-
1) ECG, 2DEcho for heart.
2) Cardiac enzymes like Trop T/I, CPK-MB.
3)
Ultrasound of abdomen for pancreatitis though normal ultrasound dose not rule out possibility of pancreatitis it should confirmed on CT abdomen.
4)
Endoscopy may require after doing all above.
Hope this is helpful to you.
If so do vote.