Wordpress Website VERY slow both front and back ends

Hello,

My Wordpress Website at https://donutfriend.com has become unbearably slow. Both when serving pages and when I'm using the back end dashboard. 

It started after I was migrated to a new server, but I can't pin it on that, really.

I've gone through various troubleshooting and Wordpress optimizing pages on here and haven't managed to make any difference. 

I can follow guides and tips, but I'm not savvy enough to figure this out on my own. Can anyone help?

Thanks in advance!

Mark