13.1 sounds like a normal hemoglobin level to me, but I'm female. The minimum normal level for a male is 13.5 according to the Mayo clinic website, so you have anemia. I'm not sure it's meaningful to call it "borderline."
The best way to increase hemoglobin is to eat iron-rich food.
Of course, your anemia is probably due to poor absorption because of your Crohn's disease. I suppose I could recommend that you treat your Crohn's, but you don't seem to be interested in that solution.
I adopted a gluten free diet a few years ago and that seemed to resolve my chronic anemia. Perhaps that's an option you'd consider.