Is it Stress?

Hi, i'm Joe, a 17 year old male who is currently studying for his A Levels.
Over the last 8 or 9 months, i have been working alot more than i had previously been working, and as if out of nowhere i developed symptoms such as: palpitations, shortness of breath, chest pain, cold hands and feet, sweating, irritability, and the general feeling that i think i'm going to die. firstly i just ignored the symptoms and just automatically blamed them on stress. But 2 months ago i just wanted to make sure, so i went to my GP, and she too believed it was stress, she then put me on a course of Propranolol 40mg daily, which did the trick, and my symptoms died down, but recently they have appeared again, i'm considering going back to my GP, but i just wanted to hear what people think before i make a decision.
Thanks
Joe :)