What are you eating the day of the flush? It's important not to have any fat to build up pressure in the liver...
Also, parasite cleansing is important. They like the liver and they can don't really want to leave. You don't have to compete a cleanse to flush, just be 5-7 days into it.
I'm a few years older than you and just finished my 23-ish (I lost count) flush. A couple have produced only a few stones but then the next was like a jackpot, so maybe you're just at that point.
Lastly, about 12 flushes ago I started using Clark's Alternate Flush #2 where I drink an additional OO/grapefruit drink in the morning (between the two Epsom doses) and have used it ever since. For me, it's like two flushes with only one extra drink.