I had a similar, less severe problem when I started cycling to work (10 miles each way). I was losing weight, and I was getting borderline underweight.

My problem is that if I'm working on something, I'll just not eat, and that's really bad if I'm burning an extra 1-2k calories (and I'd end up really low on energy on the ride home). So I scheduled regular snacks, many of them with higher carbohydrate levels than I would normally eat (yogurt + granola, crackers + cheese, etc), and I would keep high protein snacks at my desk (nuts and whatnot). I would make sure to hit my targets for protein and fat, and then go ham with tasty snacks.

When I reached my target weight, I dropped the snacks.

If that doesn't help, then I recommend what my friend w/ thyroid issues did: drink nutrition shakes (basically adult "formula"). He had a limited appetite, so he would have to get as many calories in as possible when he was hungry, and calorie/nutrient-dense shakes worked because he would just not finish larger meals.