That means, that i need to buy merit, just to rank up?
You have to earn the merits,if you are buying it means you are abusing it so you will be red tagged if you get caught for merit trading.
I been doing a lot of post, but never had a merit.
Doing lot of posts doesn't mean you will get merits,make some useful posts which can be helpful for the upcoming users.
What should i do?
Just keep doing good posts soon you will get caught in to some generous heart who will share their merit.