Well you get 1 activity for every post you make, but you can only get 14 activity every 2 weeks you're active. That means you've probably done many posts when you've been active, and then you've went inactive for a while and missed some 2-weeks period. You've also probably done all your activity gaining posts for the last 2 weeks cause I see you posted several times today, but you still need 4 more activity for member.