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Your father is having severe abdominal pain
and cause of this pain is still to be detected, gastritis
pain should respond to treatment if it is still persisting then it must be investigated.
CT Scan of abdomen with angio is good investigation it should give lot of information and once cause is known treatment medical or surgical can be done.
It is not clear that other investigations are done or not like a sonography
and blood test
for Liver function(Bilirubin
,SGPT,SGOT) and Pancreas ( Amylase and Lipase). Is there any history of alcohol use?
You should get investigation as soon as possible as if obstruction in the blood flow is there it is medical emergency.
Take good care of him