The tapeworm segments coming out after deworming can be the dewormer working. Your dosage may be off but sufficient enough to make the worms exit an inhospitable environment.
Keep in mind, it is possible for them to have multiple issues at once.
Long ago in a land far away.....My flock had Coccidiosis and roundworms at the same time. It was indeed a learning experience.
Wormers can negatively affect the flora in the gut. So the yogurt helps. But if you're in an area that's sporting 90°+, the heat, wormer and GI imbalance can cause diarrhea leading to dehydration.
This page has a number of things you can do to stop the diahrrea...