Theme wont work with prefix www.

Hello,

I am hoping someone could help me, I am using a VPS server with WHM and I recently just setup Google page speed dns and it works fine, I installed a fresh word press on the domain and everything works fine but if its just mydomain.com, I want to add www. to my domain so I added it to the admin page in settings-general, and i changed the wordpress URL and site URL to https://www.mydomain.com, it loads the website but some icons are missing and it doesn’t load the search bar basically doesn’t load it all compared to if I had the Home URL and site URL as mydomain.com. Is there somthing I missing from the DNS? I dont know what else to do please help. Thanks