If you only did one clease, and didn't follow up with another one, and then do routine maintenence, the parasites may be coming back.
People rarely take enough to wipe out all of them. There are several reasons for this. Recommended doses on the label are way low to protect the purveyors of the products. People are afraid to take more than recommended. They kill off a few germs, feel a little better, and think that's all there is to it. That's not all there is to it. In order to get rid of parasites you have to be tenacious and determined and persistent. AND, parasites have a way of making you afraid when you start taking enough to threaten their colonies. When they are being threatened by anti-parasiticals, they become afraid, go into fight or flight mode. The big ones will start stinging you and the little ones will start migrating, looking for a place in the body where they can get away from the anti-parasiticals. When they are stinging and migrating, they are afraid. That means they are emitting high anxiety fight or flight chemicals. The fearsome chemicals start circulating in your system and you feel anxious and afraid. It is a built in natural mechanism to prevent the host from taking action that will eliminate the parasite. You start thinking you are going to die. You become afraid to keep cleansing.
If you have not yet read Parasite Rex by Carl Zimmer, read it now.