Ive been having chest pains?

Ive been getting chest pains to the left side and in the centre i went to my doctor and she sent me for a chest x-ray and a Ecg. My xray results don't come back till next week but my ecg showed a fast heart rate but my doctor just told me to come back when my xray results are back but im worried any one had a similar problem and know what this could be? By the way im 24 and quite healthy.... and im not really out of breath and it happens anytime when im exercising or resting