Pain under left rib cage while breathing

I had this problem last week and after taking medicine it disappeared and later I felt tightness in my chest when I lift some weights around 25kg after that I felt fast heart beat and when I checked my heart beat rate in my mobile phone, it was showing abnormal results and every time differently, like 104, 96, 87, 45, 79 and so on. I thought it might be the defect of the phone sensor but when I check other's heart rate it's showing accurately. It's showing my heart rate stable in the morning in the range of 65-76. And in the afternoon and evening it shows abnormal. When I took ECG, 2D echo and Blood test. doctor says my heart is functioning normal. Can anyone have heart decreases even if ECG, 2D echo and HDL/LDL are normal? Please suggest. Thank you