Talk to General Physician on Chest Pain

I'm 21, 5'3,105.8 lbs It's been years since I'm experiencing breathing issue (shortness of breath), fast heartbeat, chest pain, pain in my left underarm & back (I don't remember when it started). The pain is unbearable that I've been admitted and given painkillers plus IV. Breathing issue is now kind of normal for me, I can't run or walk more than 2 3 minutes and as for stairs not more than 2 floors. 6 or 7 years ago due to the same issue I was taken to hospital and my chest x-ray and other tests were done I don't remember the doctor's exact words but my oxygen level was very low. Many physicians think it's because of stress or digestive issue but I don't really think this is the reason.