I have been able to control my IBS via diet, I've eliminated most grains from my diet and eat homemade yogurt (plus take acidolfulius(sp?) pills as well).
The template for my diet is the SCD diet (i made my own modifications with some experimentation) you may want to give it a shot
www.breakingtheviciouscycle.info
For me, the best thing to combat fatigue is (strangely) working out. Running/aerobics works the best for me but even walking for a half hour helps.