Hi,
Welcome to health care magic,
Stomach bloating is caused mainly because of air swallowing known as erophagia.
The other causes are
irritable bowel syndrome or dyspepsia or
constipation or peptic ulcer which needs to be diagnosed by clinical examination and various investigations.
If you already started tab.nexium and still having
abdominal bloating or distension then you should continue that antacid medication or take
pantoprazole or rabeprazole with antacid gel like digene or sucralfate,
avoid excess carbohydrates and fatty foods,
avoid oily and spicy foods.
If you still have these problems then you should go for routine blood tests with ultrasound abdomen and upper GI endoscopy if had not done earlier.
MRI scan have not much role in this type of GI symptoms but endoscopy can give some clue if you have a problem since long time.
Feeling of ball under rib cage should be due to this gas trouble or stomach bloating but X-ray will help to rule out any other bony abnormality.
Consult to gastroenterologist again and ask for various investigations to treat underlying cause.
Regards,