What Causes Constant Fatigue Post A Colectomy?

I had a colectomy in 2012 due to severe complications with ulcerative colitis. My question is, is it common to be still suffering from severe fatigue? I m 28 years old and I feel myself wearing out a lot easier than I used to. I m still very active. I work out regularly, about 4-5 days a week, ride dirtbikes, snowboard, hike, etc... I know I have to supplement with vitamins and stay hydrated, which I do but it seems after the surgery, I ve noticed that I don t have the energy that I used to. Please any advice and information is greatly appreciated.