I also did my second flush just a week after my first and got nothing out but a bowl full of what resembled pea green soup and no stones.
I waited two weeks and a day and did my third flush last night with great results....probably 200 stones and a grand prize stone that was the size of a Robin's egg...is was both green and tan mixed.
Although I was more careful on my second flush and immediatly went to bed and fell asleep on my right side...I would think it was the 2 week wait that allowed the stones to build up again.