After many hours of searching, I found it! It's Mississippi Fred McDowell...and it's Good Morning, Little Schoolgirl!

Things is, I knew that song by Muddy Waters, but I never searched for it now. I was just browsing McDowell (from the beginning I suspected it was him or Blind Willie Johnson), was listening to one of his records and it suddenly came up.

Much thanks to everyone for this one. I love this song.