My heart has been feeling funny!?

Ok i have all ways seemed to have this thing wrong with my heart i think it maybe be excited related its like when i really think about it it happens and lately its been randomly showing up i will be sitting down and then when i get up my heart will be pounding and i will be gasping for air and have to stand still and let my heart slow down. im 16 and 140 pounds its really started one time after i smoked weed i am done with weed for good after i freaked out at my friends house and had to go to the hospital, and i all ways have this itch felling in my heart i have seen a heart special lest about this but it seems that nothing is wrong help