Please help weird heart problems?

im 15 and i have a weird feeling my my heart its almost like when you're on a roller coaster and you down down a steep drop you get that feeling in your stomach but its less intense i went to the hospital and told them so they did all their stuff hooked me up to their machine (they put stickers all over you and then it prints out of piece of paper) i forget what its called EKG? the doctor read it and said everything was normal and that i just had anxiety but i think it might be something more serous because i feel it all the time and i have chest pains like 1 or twice a week what are possibilities and what should i do? my left arm is also starting to get the sensation it just feels really weird and uncomfortable