Not only do you have to actively post high-quality posts, it also takes a certain amount of time to reach a higher level.
You have to register for at least 126 days to get 120 activities
activity = min(time * 14, posts)
It is recommended to read this post first
Newbies - Read before postingActivity is increased by posting and is updated every hour; however, the updated number of activity points will be reflected at your profile at the end of the current activity period. As a note, in case you have latent activity points from earlier periods (meaning activity periods where you didn't post daily: in this case, the days when you did not post become latent activity points), these ones will be updated on your profile after 1 hour. You can gain a maximum of 14 activity points every 2 weeks.