I was a regular, Then Automaticly I'm a member! CRAZY.
You probably missed a requirement to stay a regular! Don't worry, you can earn it back by being more active and reading more topics and posts.
You were really inactive for a while. That might be why.
Not reading enough posts, topics, being on actively enough, flags etc. This is called demotion when you go down a rank, like in your case regular to member. But no worries!! You can earn it back again by being active, reading, staying on topic, not getting flags, etc.
I know, Demoted and ranked.