In the UK the doctor can order xrays and other imaging like ultrasound scans, barium meal xrays, and would refer you to a specialist
for a colonoscopy and any other tests to check
for problems in the digestive system.
The doctor should also consider doing blood tests to check your kidney and liver function.
A stool test can also be done to look for any bacteria (especially Helicobacter Pylori), parasites and any more serious problems.