I went through concord and helped Preston to Sanctuary. The thing is that I didn't speak to Mama Murphy before I left. Now she doesn't show or say anything about "Dog". Is Dogmeat forever named "Dog"?

I am running into the same issue. I believe there is one only one shot to get the name Dogmeat.

I don't wanna spoil any story, but you do get a second chance later on, I know because I didn't talk to mama either