How Can Sternum Pain With Cough Be Treated?

Hi, i have had a sort of chest popping thing going on for years now, that when i stretch back i feel my sternum pop. It always was brought relief to the stiffness. Recently though, i cannot pop my sternum and it just seems to be a dull ache when im in certain positions. Tonight for example, i was slouched over on the computer and noticed it bothering me and i coughed and got a sharp pain in my sternum. But when im standing straight and cough it does not seem to bother me nearly as much. I have bad anxiety and worrying about this is not helping lol. PLease help doc