The very reason why we do a two sessions enema is because the first session helps expel stuff, while the other (with probiotics you want to keep in so as to repopulate the friendly bacteria and kick out the candida) stays in and helps rehydrate the intestines.
All the candida and the toxins we expell while cleansing are damaging to the bowels, and to force the bm out reduces the time allowed for the big intestine (colon) to reabsorb water, so your metabolism is keeping the second enema in order to rehydrate.
On the second issue, nothing coming out, did you do the enema after a bm or do you mean you suffer from constipation?