My computer is running unbelievably slow after installing Avast. Need help.

I just purchased a new laptop. On my old computer I was using Malwarebytes and Microsoft Security Essentials. On my new laptop, I got Malwarebytes Pro and put Avast. Now my computer is going even slower than my old computer, which I bought six years ago! Downloads, uploads, watching videos, and even just browsing the web is slow. I don’t know what to do. I need some help with this. It’s too slow for me to be able to use it.

did your new computer come with a preinstalled AV from factory?
did you remove this, uing that vendors removal tool before installing avast?

Running the uninstaller right now and will report back on the speed of my computer as soon as it is finished.