The cholecystokinin which is the CKK is the hormone that is normally secreted in the duodenum in response to a fatty meal. It causes the gallbladder to contract increasing the flow of gallbladder bile and liver bile. The pain you felt during the test can be a spasm (like cramp) as the gallbladder tries to contract but the it is full of stones. The brain can't delineate the source of pain inside the body so you get a referred pain pattern.
There are other condition that cause the pain such as a blocked bile duct but this is much rarer.
The 'stones' in the gallbladder can often be very soft and do not show up on a ultra sound examination. The 'stone' at the neck of the gallbladder is whats called impacted and this causes the blockage at the point where the gallbladder joins to the bile duct. This stone can harden because it is washed with hepatic bile during formation; hepatic bile contains calcium.
Four flushes must has done something as you've expelled a commendable number of stones. It's difficult to keep going but you may need many more flushes. I needed about 16 flushes to regain function of the gallbladder and many more to clear out the stragglers. I think I got rid of the last one this year; no more pain and no more fussy eating.
A gallbladder with such a low contraction as yours is not going to push out the stones quickly. So keep flushing a researching.