It sounds like your medication is pooping out on you, this happens and is normal. Our bodies build up a tolerance for it over time, and we need to switch medications. Call your prescribing doctor and let him know how you are feeling, he will know what to do.
Hi, I had something very similar too, like a fullness in the chest and breathing gets shallow and cant eat etc etc. I think it is anxiety related symptom, specially as youve had lung tests which showed no problem.. I would try to de-stress like yoga or meditation