You have got evaluated for your heart and the echo seems normal.
Also you have got your endoscopy
done and it rules out any ulcer disease.
The symptoms that you are describing can be a lot of times because of some nerve injury
that must have taken place during the c section and hence now causing restricted diaphragm function.
Another thing that i feel you can have as you have back pain
and restricted movements in the morning can be an ankylosing spondylitis
Get a xray spine and a usg of the abdomen to look for diaphragm movements and then see a physician