'Stones' can be all different sizes...really small like a grain of millet all the way up to a golf ball!
You can do enemas as often as you need to...I usually stick with purified or distilled water or coffee enemas...but some people have good luck with lemon juice, baking soda, Epsom Salts , acidopholus, wheatgrass, etc. For constipation...plain water is probably the best. If you're backed up you should probably reduce or stop the shakes until you get things moving again.