Nayda,
I find 2nd Lt J. W. Chivers as a company officer in Co B. It appears he was not a military doctor. It was not unusual for a doctor to serve as a line officer if there was not a spot for a doctor. At the start of the war it was first one there and selected by the commander of the regiment as the surgeon, later in the war they had to meet a medical board.
There where 2 Surgeons (S.T. Hunter and & W.C. Wathen) 3 Asst. Surgeons (S.P. Cargill, Wm. Stelfox and F.D. Cash) listed for the regiment.
MikeT