permalinks not working properly

Hi

I have created a site with pages and posts. I added the permalink plugin so my URLs are not random ? and numbers etc.. my pages work fine but my blog posts URLs seem to duplicate.. So when I go to my blog, the url is https://www.mydomain.com/blog and when I then click on one of the ‘posts’ (which I named ‘testing) I get a 404 error as the URL says: https://www.mydomain.com/http:/www.mydomain.com/testing/testing

I cannot get it to work. Can anybody recommend anything? My custom permalink structure is https://www.mydomain.com/

I also noticed that I cannot upload images to my Media Library and when I install a ‘breadcrumb trail’ it says Blog > About etc, rather than Home > About

Any assistance would be much appreciated as I’m pulling my hair out trying to figure out what is wrong.

Many thanks