Did you have this smell before starting the parasite cleanse? If not, it could be the powerful ingredients in the mixture. Plants that are highly toxic for parasites are mildly toxic for humans, probably quite toxic in certain doses.
Also the black color of your bowels is not necessary linked to the removal of parasites; it might be the mixture you are taking. Some foods can color your bowels; I panicked several times about weirds colors til I remembered I ate foods of the same color the day before. Try beets for instance!