Trouble Breathing?

So the last few weeks, like 2 or 3, ive been having trouble breathing, it feels like im not getting enough breath. like i have to gasp ever so often. i have had some chest pain, but it feels like i have dislocated a rib or something not just around where my heart is. this has happened before around 4 years ago, and i got my heart tested, my lungs tested and all that stuff. And they couldnt find anything and said i was healty. I have exercized and ran and it feels fine when i do that stuff and also it only happens relaly when i think about it, ill be like yes im not breathing heavy its good to breath normal aand then it will start to happen again. it hasnt happend again since now, i was wondering if anyboyd has any idea what it could be. or if i shoudl go back to the doctor to have them run more tests.