I saw your post and thought I would give findagrave.com a look-see just in case he is listed there.

Jackpot! This is what is says: "Samuel W. Williamson, Birth: unknown, Death: Jan. 30, 1865, Note: Served in the 21st South Carolina Co L. Wounded at Ft. Fisher & died enroute. Name is not listed on monument but appears on a list from Baltimore National Cemetery updated May 25, 2006 located at the monument. Burial: Point Lookout Confederate Cemetery, Scotland, St. Mary's County, Maryland, USA"

You might check to see if any website about Point Lookout has headstone photos or can get you more info. Good Luck!
Kerry