You have a rather complicated medical history. GERD, chest discomfort, and breathing problems can all go together for a person with a dx of GERD.
You also mentioned you had a problem with your thyroid in the past; I would recommend that you see your Dr. re all the issues you have going on.
Another cause of
chest pain may be costochondritis. With costochondritis there
is inflammation in either the costochondral, the costosternal or the
costoclavicular joints (or a combination). Costochondritis causes chest pain,
felt at the front of the chest. The pain is typically sharp and stabbing and is
worse with movement, exertion and deep breathing. Pressure over the affected
area also causes sharp pain. The pain is usually confined to a small area but
it can spread (radiate) to a wider area. The most common sites of pain are
close to the sternum at the level of the 4th, 5th and 6th ribs.
Remember I am not a Dr. so please do check in with your Dr.