I've encounter the exact same problem dozens of times my friend,
I have carried out over 60 flushes at this point, and I have had times where I would go for a three months without one stone coming out,
This all ended once I started using Gold Coin Grass in tincture form from sensible health. It is transported right into the liver with the little bit of alcohol that is mixed in with the medicine. I could feel the symptoms subsiding within two days of taking it, so I knew more bile was getting past, which meant that the stones were shrinking or breaking into pieces.
Since using GCG, I have gotten tons of material out every flush and have sped up my progress two fold.
Let me know if you get some and what your results are!