Hi,
Generally, liver doesn't feel pain even if it is severely damaged. That's the tricky thing because it can be extensively destroyed before you know it (and usually it is too late).
In my opinion it is a gallbladder stone especially if the pain is excrutiating. Is the pain located on the right side just before the ribcage? Radiating to the back?
However, it can also be caused by something else like pancreatitis (in this case the pain concentrates on the left side of the abdomen, but there are no strict rules). There can be other causes as well.
Anyway, my advice is that you should contact your doctor asap. Do not wait.
Kris