This might be either gastric ulcer or some blockage in biliary/pancreatic tract.
And either way gastroscopy with ERCP should be performed as soon as possible (it will rule out both).
Before it, you should have blood tests with hepatic and pancreatic enzymes done.
is necessary if acute pancreas inflammation
will be recognized or when gastroscopy/ERCP will show nothing.
Until this test you should keep hepatic diet.
Hope this will help