Very interesting about your stone getting larger. If you want my guess on what is going on, I would guess that the stone is actually breaking down, the components of the stone are loosening up therefore making the stone seem temporarily larger. This increase in size may be what happens before it breaks open into small gravel and sand.
I would be very encouraged if I were you. My recommendation is to keep taking stone breaking herbs. I have also felt like yoga stretching and compressing is good for the vital organs and encourages bile flow.
You will get this stone of yours, I am sure of it. Do not give up!