Please help, my SEO work is in trouble

Please help, my SEO work is in trouble

Hello everyone, first I would like to send best wishes !
I am beginning to learn SEO
I am seoing and developing for a website that to provide services mosquitoes,
name written in my language "cua luoi chong muoi".
my site is [cuamuoi.com]
I have seo for 2 months with keyword "cua luoi chong muoi, luoi chong muoi." for this site
A friend also SEO those keywords with a different websites domain name as [cualuoivietthong.vn] - 2 our website by a coder,
domain name and hosting with the same provider.
Weird when examining Google keyword rankings;
if my site have Top on Google, website of my friend will missing . And vice versa. swap just happened in 1 week,
current top of it up very slow speed. you are the professional seo, has extensive experience please give me some advice to solve this
thank you!