Dear freind, welcome to HCM.
sternal / chest trauma
can cause bony pain, or may occasionally cause diaphragm (breathing muscle) to rupture and hernia to develop toward chest.
to differentiate it from here is difficult.
you were right in seeing a gastro enterologist,.
just ask about hiatal hernia, diaphragmatic hernia
and plain GERD
, ulcer etc.
then may be bony fracture
etc. would be thought of.
I think I can offer this much now.
keep me posted on what happens.
take care and good luck.