I would say it might be b12 / iron since I'm getting these sores at the corners of mouth.
Sores at the corners of my mouth went away when I stopped using toothpaste and mouthwash. I checked with my dental hygienist and she said it was really the brushing, not the polish, that cleans teeth. 2 years, 2 more hygienists and 2 dentists (we moved) have all confirmed that my teeth are fine (I floss 1x/day and brush 2x/day).
Not that it couldn't also be b12/iron issues, just that this helped me a lot! Full disclosure: I am consistently, barely below normal levels for my iron (have been since childhood).
On exercise, check out the greenling post with lots of responses on this sports/fitness forum about starting workouts again - consensus is that we recovering celiacs may need more rest days than we used to for our muscles/bodies to recover. So think about bicycling but perhaps not as many days a week as you would have 'once upon a time' - see how that goes.