Is it all in my head?

must things i think happen or does it example i keep thinking something wrong with me heart so i get little chest pain and little jumpness, or a nother day i would think about how i feel and then i think i feel weird or im going to go dizzy, or callospae, i think my hearts racing its going to stop. i always think something wrong with me as that how i feel inside but i dont get really any really syptoms, i went to one doctor and he was laugh as i was worrying cause ive lose weight and im normal size, he just said it anixty and never gave me any blood tests, i worrying cause im 19 and have a 10 month daughther and dont want to go mad or mental or drop dead.help xxx