My Mac won’t let me log in even though i didn’t change my password.

I shut down my mac, and turned it back on like normal but for some reason my wallpaper changed to the automatic one and, instead of having me log in with just my password it now is asking for my name, and password and i put in both and it still won’t let me log in an says its wrong and i tried restarting it as well but no difference and when i shut it down again a pink screen flashed so i’m not sure if that means something, and yes i have tried doing the resetpassword thing but it wouldn’t let me. This is the first time i’ve seen something like this so i’m not quite sure what to do.