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
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.
Take care.