The most probable cause to your problem is the whole ToriClan fiasco that's been happening recently.

Stuff happened with the ToriClans and their DSCs, which probably caused the drop in your post count.

A vast amount of posts were either moved or deleted, mostly from Clan Discussion.

As for getting your post count back from the DSCs; I'd send a PM to a clan moderator for more information.

A section for clan moderators (users with black names) can be found here.