The first page is an end page. I couldn't resolve it.

[Spark]

Hello valuable forum members. About 3 months ago, I had a website made. The site comes to the 7th position on the first page for 2 days. Then, it drops back to the 80th position. A week later, I check again and it's back to the 10th position. Why do you think this happens? I have a reseller server. I have 4 sites with the same keywords. Could this be the reason? The other 2 sites are always in the same position, their rankings don't change.