Fatigue is a byproduct of all the stress put on the body by AS. When I was able to take an anti-TNF, it took away all my AS pain, so my fatigue disappeared as well. So, if you respond well to anti-TNFs, then you can expect your fatigue to diminish also.
AS symptoms started 1991. Official dx in 2006 with HLA-B27+, fused SIJ, bone spurs in back, extreme rib/hip pain, and other family with SpA. Started Enbrel in 2006 with good results, but stopped in 2010 due to nerve damage (MS) from it. Now getting good results with no-starch diet.