Jimmy,

This is Thomas M. Nelson's record - he was from Doughtery County - he was the surgeon of the 4th.

Nelson, Thomas M: ---- private April 28, 1861. Appointed Surgeon May 10, 1861. Resigned November 4, 1861. Elected Captain of Nel son's Company Ga. Cavalry April 18, 1862. Appointed Major of Corps of Scouts and Guards, C. S. A., June 27, 1864. Elected Lieutenant Colonel of the 6th Regiment Mississippi Cavalry July 1864. Killed at Tupelo, Miss. July 14, 1864.

There is a J.D. Nelson listed in the compiled service list, but not listed in a company - I also could not find it in the Doles-Cook History book that includes the 4th Georgia.
If this is your ancestor, your best bet is to go to the Georgia archives to search for his records; however, he is not the surgeon, as Thomas M. Nelson was. If I can be of more help to you, please contact me at remgaconfed@aol.com