The first page is the same as the last page. I couldn't solve it.

[Spark]

Hello valued forum members. About 3 months ago, I had a website created. The site is ranking 7th on the first page for two days. After that, it drops back to 80th place. A week later, I check again and it's back at 10th place. What do you think could be causing this? I have a reseller server and I have 4 sites with the same keywords. Could this be the reason? The other 2 of my sites are always at the same ranking and their positions do not change.