I run cross country (5K), and at a couple meets last season, I ran and felt well the first 2 miles but then hit a wall and could barely keep my legs moving. I felt totally gassed with no energy left. Have you seen this problem before and what could it be?
It sounds to me like you need to try eating something small closer to race time. I struggled with the same issue in college and found that it helped a lot if I ate a banana about 30 minutes before start time. This was in addition to the oatmeal, toast, coffee and water I’d have about 3-3.5 hours before start time.
I would suggest experimenting before hard workouts and races to find the right timing and the right fuel for you. Everyone is a little different. Good lucK!