Have you got anything running in the background. A virus checker or the like. I use AVAST.It's icon is in the task bar and it rotates periodically as it checks files etc.
When the system slows bring up your 'Task Manager' and check what's running.
Xiaomi Mi Mix 2 review
See mcbess's iconic style animated for Mercedes-Benz
iPhone X news: Release date, price, new features & specs
Black Friday 2017 : date, sites participants & bonnes affaires