I have this strange light pain in my left axilla almost towards the back & shortness of breath what can it be?

Not enough info: To narrow down the possibilities, one needs more information from you. For example, if the pain increases when you take a deep breath, it is termed "pleuritic", meaning it suggests pleurisy (inflammation of the lining around the lung). However, viral illnesses, pneumonia, even more serious problems such as cancer, can cause pain and shortness of breath. You should be examined by your doctor.