Why does my heart or chest hurts!,?

it happens every time i think of some stressing stuff but it goes away and when it hurts is difficult to breath so, i take a deep breath and then it kind of starts going away. i think i felt this before when i was pregnant, i don't know if is like anxiety and i try not to think on stressing stuff but sometimes i can help myself and i wish i could tak some medication since is really annoying!? what is it and what can i take!