Why did my activity stopped increasing, what could be the problem, please I need help.
There is no any problem.
The forum is designed to be like that because number of activity is among the criteria to rank up in the forum despite your number of merits.
One activity on daily basis, but it is designed to stop at fourteen till after two weeks, which means before you can get a high rank in this forum, you will be in the forum for sometimes so that you can understand what the forum entails and you can interact in the forum with other users.
Read this thread to get some basic information you need to know about this forum.