I just finished the quest to get Nick Valentine. Went to Sanctuary to stash my junk, but when I press on the Workshop, it tells me, "You are not allied with this settlement." Same with Red Rocket and Tenpines Farm. Reloading does not help. Did I do something wrong? Or do I need to start a new save?

I'm stuck and don't know what to do!!! I lost control over all allied settlements too.

I took the castle after noticing this and now it's the only place I can access the workshop. I tried loading the save file from a different PC, same thing happening!

Any solution to fix this is much appreciated. Thanks in advanced.