Google ranking different unrelated pages daily
I have a problem with incorrect pages of my website suddenly ranking/changing daily for unrelated search terms.
For the past 1-2 years my website has ranked quite well for a wide range of search terms. For the past 1-2 months I have noticed that lots of unrelated pages are now ranking for some of my most popular searh terms on a daily basis. I have not made any SEO changes in the past few months apart from I have lost 2 or 3 incoming links. I have not changed the internal link structure of my website and just cannot figure out why suddenly so many unrelated searches are ranking and even more strangely changing daily.
Example:
www.mydomain.co.uk/blue-shoes used to rank well for the search 'blue shoes' but now, every day a different page is ranking for 'blue shoes'?
Saturday:
www.mydomain.co.uk/belts ranked for the search term 'blue shoes'
Sunday:
www.mydomain.co.uk/large-suitcases ranked for the search term 'blue shoes'
Monday:
www.mydomain.co.uk/delivery ranked for the search term 'blue shoes'
Tuesday:
www.mydomain.co.uk/plastic-wheels ranked for the search term 'blue shoes'
Does anybody have any experience of this happening to them or know why this is happening?
Thanks