Activity will increases when you reached the 14 points.
When you post a post in a Day 1 points will increases, I think you are not a daily poster. You post one day and then dont post for two or more Days. This would be the only reason that your activity is not raising.
I started posting Daily, so will that make my activity rise..
AS only a few days ago (Maybe a Week or so) i started actively participating the forum.
You're not going to get any more activity points until the 17th now. You need to make sure you post at least once in every two week period. If you don't you'll lose those points forever.