I have been visiting the site from more than 30 consecutive days, but I haven got enthusiast badge, why?
And also wanted to know,
For the fanatic badge, its 100 consecutive days, would you get 3 enthusiast badge before getting fanatic badge?
You've only just got to 30 consecutive days. The badge system can take a little while to pick these up. Wait to see what happens over the course of the next 24 hours.
Also note that you can click on the "visited" field in your user profile to get a calendar that tells you what dates you visited.
The Enthusiast badge is awarded only once. So you would get this badge a short time after you visited for 30 consecutive days, and if you exceed 100 days you would get the Fanatic badge.