I will be grateful if anybody advise me what can I do in this condition?

I created some sites for adsense.these sites are between 1-20 position in search engine for specific keyword.Some time I found a site in position 5. Then after 2-3 minutes when I search with same keyword I find this site in position 11-12. I can not understand why this fluctuation occur? I got same result for my all sites. Sometimes it show 7-9 position.After next search it show 12-16 position and become steady in 12-16 position.
The keywords are very low competitive.

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Stag Do