Why can't I find my posts when I login?

Are they deleted after a period of time?

They’re still here. Just not findable through this tool. The cut-off is a few months (3, I think).

You may find specific older posts though the internal site search,

or perhaps easier: through an external search engine (e.g. Google), with keywords like:

site:discussions.apple.com "werdup"

You can find your recent posts through the Profile icon in the upper right corner (on computers). The pop-up gives links to various pages related to your profile. The My Subscriptions link will get you to a list of threads that is a combination of following topics (sub-forums) + subscribed threads, participated threads, and authored threads. You may use the Filter on the left to narrow the results. Any of these can be bookmarked/​favorited for easy access. Participated threads are marked as subscribed automatically. Authored threads are included in your participated threads.