My husband and I just finished a flush - his first. He had the same thing happen with the cramping beginning about 1 hour after taking the first dose of ES and continuing most of the night. Also he did get out some stones but not all that many and not until later in the afternoon/evening. The clear water squirts didn't begin until late afternoon whereas for me it was nearly clear after the second BM the morning of the flush. It appeared that his bowels were more backed up and had some difficulty removing material. I'm in favor of him using a bit less ES next time AND working on cleaning out his bowels more beforehand. But I'm not sure he'll volunteer for another flush at this point.
Not sure about your case since you've done flushes previously. Is there a chance that your bowels were more full than usual?