06 Mar 17 6:59 am
The primary factor of fluctuation in ranking is Google updated on the algorithm, each and every day they are trying something new to better results to the users.
There are many other factors included as well from your side
If you have crawling issue, Hosting issue, changing on the Onpage, keyword mapping, Changes from the sites which you have used for link buildings, changes in competitors SEO strategies.
Especially if you have tried any blackhat techniques, you will get frequent fluctuation. Search engine optimization is the ongoing process, and you have to ensure your quality effort regularly to get stable results on SERP.
You can clearly see there won't be any notable changes in other search engines like yahoo, Bing.