While there can be a number of possible explanations to what happened, my intuition tells me that in your case you may have sent out a bunch of backlinks that have now either taken a backseat or have got deleted (did you physically visit the link pages and check?). By the way, if that's not the case then it may be a simple Google dance - something that bounces new websites up and down. In that case, keep building backlinks consistently and it will work out.

And not only that, but the internet is hardly standing still.

Google does not make billion$ by being stagnant.

Once your site gets a little authority, it's stays in a normal region. Maybe.

But there are no guarantees.

Search results change depending on search terms, time of day, what's in,
what's out, who's searching, etc.

Paul

Google Dance.

I mean....

Google have been monitoring your progress specifically, and have manually changed their algorithm so that only your sites rank lower. Since they dislike you.

But seriously, it's the Google Dance. It's nothing personal

I know my competitors are not sleeping, but it should get fluctuate from 10 page to 12 page, but why my link is not stated even within the 50. is it bored.

These kinds of changes in Google results happens and you should not be worry about it. If the crawling and indexing your pages has been changed, you should be worry and think about penalization, but changing in ranking is natural IF it takes only for some hours.