Welcome to my world. I can never eat on the first few days of an intense hike. By far the best way that I have been able to get calories is by drinking them. Gatorade, Koolaid or my personal favorite Maltodextrin. You are describing exactly why I started drinking Malto, long, intense days often at high elevation. I couldn't eat a thing and it became downright dangerous as I was doing long shoeshoe trips into the heart of the Sierra. i keep thinking that I have overcome this but even as recently as a year ago I couldn't eat anything on the Colorado trail. Malto was my savior.