Why can't I edit my own post?
When I click Tools, the edit is grayed out.
And what is Purge?
How is it different from delete?
@harveyab you probably ran into the limitation for posting too often. There is a limitation that users with less than 2 reputation have to wait a certain time before they can post again (anti-spam measure). I think the edit works with the same counter.
Purge will remove the topic, if you are the original poster. Delete will only delete that post (can cause some weird looking threads if the original topic post is deleted)