No after 14 days going up for every one 

Yep! as far as I know, each post or thread counts as 1 activity point and you can only a max of 14 activity points for every 2 weeks.

I noticed you joined more than a month ago, if only you were active all these days, you'd have 48activity points by and would be a Jr. Member.

I want to know how my activity increases?

Thanks, it is fine if a person creates an activity calculator.

Not like it. Although I did not realize how does it work exactly!

Not necessarily from this point in time. Activity updates for everyone at the same day/time. There is a list of the future updates that can be found here.

It does not drop.

It's simple , because you get a maximum of 14 activity per two weeks . You should wait for the next activity reset (each couple of weeks) to get your activity higher .

Why do people keep asking about this? I think we should make a video (or something) to make people more understand about this.

I was just lazy, and the 30 seconds to get a response was faster than sifting around.