Sorry for the delayed response, I was on vacation.
There is always the possibility of a bile duct stone, even after the gallbladder is removed.
If this is suspected, the test of choice would be an MRCP or ERCP, which are tests that can evaluate the biliary tree. If indeed there is a stone, the ERCP would be needed to extract it.
Otherwise, further abdominal imaging needs to be done to evaluate the source of the fluid. A CT scan should be considered, if it hasn't been done already.
These options should be discussed with your personal physician.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin Pho, M.D.
KevinMD.com
Twitter.com/kevinmd