This very simple as you have been diagnosed, it is cholelithiasis (stones in gallbladder) with on and off biliary colic (pain related to gallbladder). So there is no test to diagnose what type of stones they are until and unless you do not remove the gallbladder surgically and then send the gallbladder with stones for pathology.
I am amazed that you did not remove it surgically and why are you getting the surgery late it will increase the chances of complications. Surgery is simple and common so good general surgeons are well versed in it. My advice get surgery done asap no if and buts.
These are some of the complications you can get if you do not remove the stones and they get trapped somewhere else cholecystitis, cholangitis, gallstone ileus, pancreatitis and many more even I can name some more dangerous ones but I am not.
I am telling you some good surgeons try anyone:
Shifa international islamabad Dr. arif malik, dr. mussadiq khan, dr. faisal saud dar( I have personally worked with him so can assure you he has great hands).
So in summary get surgery done to avoid these pains you are having or any further complications.