Hello Since you are a female with 23 years age , E K G normal , still pain on the left side just from 2 days and aggravate during breathing , standing or bending forward, these symptoms may be due to these possibilities , these includes. 1 The 1st possibility is of pancreatitis as it may cause upper left abdominal pain ( simulated as in chest) which is worse when bending or sitting or standing . Pancretic enzyme like serum amylase & lipase should be measured to rule out any pancreatic cause. 2 Pneumonitis or consolidation of the lung on left side may be the another such cause . Get in X RAY chest pa view to rule out lung involvement. 3 Hyper acidity or acute gastritis may be the another such causes . For this just clinical history of illness and physical examination by physician is sufficient. In my opinion deal as I mentioned above. Good luck.