The clumps are almost certainly stones. Next time, look and see if they float. Most stones are either tan and bumpy or smooth and green. Some of the bumpy tan ones are smooth and green inside if you cut them.
Acid: Can be reduced if you drink lots of water the day of the flush, except for within 20 minutes of any of the drinks. Acids are toxins moving out of the liver. They seem to be strongest at the beginning and end of the appearance of stones. If you have pain there, I've heard that you can cover the offended area with petroleum gel (I hesitate to add anything from a petroleum source to my skin, but others have used it) or olive oil (I've done the latter, it works if you reapply each time), or I found that gently patting the area with a cloth soaked in coffee also soothes the skin.