I would go to or ring the hospital and ask if they have a specialist doctor who deals with gallstones (I don't know the what the specilaist name though it may well be a
gastro-enterologist) and then ask if he normally works at that hospital.
If you ask AEK, they may well say we have Dr so and so who comes here 2 times a week. That is your clue that he isn't normally based at that hospital. In which case just ask them where he is based and his contact details.
If it is a gastro-enterologist, PM laphanphon, he knows the name of the gastro-enterologist based at Udon hospital, who he and I have both seen. I can't remember his name -( short term memory loss comes with age).
This is a Google search link on the topic of gallstones which may help:
http://www.google.co.th/search?q=doctor ... =firefox-a