Google Analytics settings no longer tracking domain & I can't add a new one

I was tracking one domain, then changed the domain for my site, then added the new one into my WordPress set-up and for no apparent reason (or at least I don’t know what I’ve done), it’s gone back to the first one and won’t let me add the new one in.

I’ve got the latest version of this plugin, and even tried uninstalling it and starting again, but it’s still only sticking to the original plugin. Help! 🙁

(However, since the author of this plugin never bothers to look in here, I figure he’s not going to help)

https://wordpress.org/plugins/google-analytics-for-wordpress/