It appears that your soldier was stationed at Mobile for much of the war.

Here is what Dr. Ken Jones' webpages at http://www.tarleton.edu/~kjones/alregts.html says:

21st Alabama Infantry Regiment
The 21st Alabama Infantry Regiment was mustered into service on 13 October 1861, in Mobile, and remained at Hall's Mill and Fort Gaines until ordered to Fort Pillow in March 1862. [...] In the summer [of 1862], the regiment was ordered to Mobile and was on garrison duty at Fort Morgan and at Oven and Choctaw Bluffs. [The regiment appears, from what I have read, to have remained in that vicinity at various forts for the rest of the war. See Dr. Jones' pages for more info.]

Echols' Company ["Swanson Guards"], 1st Alabama Conscripts

The 1st Alabama Conscript Regiment was formed in April 1862 for six months. It was stationed at Camp Watts, near Notasulga, AL, until the end of the year. It was commanded by Major William G. Swanson and consisted of ten companies. Echols' company, the 'Swanson Guards,' was formed the following year from detachments of the 1st Alabama Conscripts. It was commanded by 1st Lt. John H. Echols and stationed originally at Montgomery between April and August, 1863. The company was transferred to Fort Morgan that fall.

There is microfilm produced by the National Archives on the PACS surgeons, and you may find additional information on his service in that microfilm. I'd also look at his record in the microfilm for the 21st and Echol's. The Birmingham Library and the National Archives branch in Atlanta should have all of this microfilm available or the records can be ordered from the National Archives.