I think the only way to detect gallstones is to get an ultrasound.
I am in the process of seeing if I have any gallstones or biliary blockage by doing a cleansing diet composed of the following and then liver flushing.
egg yolks + lime as my main source of calories
Chinese bitters and Gold coin grass in the morning for dissolving the stones
Castor oil packs for an hour a day on the liver for disturbing anything clogged in the liver/gallbladder area
Coffee enemas to further help get bile flowing
Grape bitters taken before or after meals
Apple cider vinegar taken before meals and especially the few days before the liver flush
This is just a few things you can do to enhance liver/gallbladder cleansing.
Some people swear by liver flushing and others believe it is dangerous and can possibly move a stone into the common bile duct which would necessitate surgery. From the reports on curezone it seems that very few ever have problems flushing and I haven't heard one case of someone needing surgery because of a liver flush.
There is a discussion board here -http://www.curezone.com/forums/f.asp?f=447 on liver flushes where you can read all you want to know about others experiences.
There is also a survey of about a 1000 people who have gone through liver flushing with the reports here -
http://www.curezone.com/faq/p/s.asp?a=28,571,2826&s=21There is absolutely no consensus and no clinical trials and multiple varieties of liver flushes though the most commonly used one is the Hulda Clark flush.
I have completed two liver flushes with no stones being removed, though I didn't follow the recipe and ignored the epsom salts. I did have a powerful headache(stronger than any in the past several months) within a couple days of my last flush so I might possibly have moved some sludge around and not out.
Many people will flush dozens of times and its generally recommended that you flush until you get 3 consecutive flushes with no stones. Though some people think the mixture (olive oil and citrus) combined with the bile is what leads to the green stones that so many people report. This does make sense to me but does not explain the black stones or the calcified stones that some people report getting out.
Many people here have done the flushes with mixed results.
You can scroll to the bottom of this man's blog to read about his incredible journey flushing
http://curezone.com/blogs/f.asp?f=1196It took him 50 flushes to get out the stones. The one big issue with most of these people flushing is that they have horrible diets that they return to and may prevent them from ever removing all the stones.
This is just a small piece of what you will find on curezone. Most will recommend a low-fat fruitarian-esque diet or even juice diet before flushing and since I don't really like think this is healthy at all I am testing whether or not this predoimantly egg yolk diet will replace all the fruit.
Also, blood tests can show issues with the liver. Bilirubin, ceruloplasmin and copper levels are indicative of whether or not there is biliary insufficiency.
Your fast could have somehow started a healing process where stones or sludge where being removed. Thats just a guess but you would be best posting on curezone and see what those more experienced have to say.