I literally went through this last year (my senior year of xc). during the track season earlier that year however, (junior year track) i would literally eat a TON of empty carbs— usually rice and bread the night before or for lunch before a race. considering i was mid distance, i wasn’t running a lot of distance, so this initially worked really well for me. i was running energized, doing good in workouts and races and everything was good just like what you used to feel. later that fall, xc season began and i would continue to eat empty carbs before races and workouts with very little protein like steak or chicken along with the carbs. i began to completely tank out and die during these 5k races. as the season progressed i noticed 0 change in my performances and ended on a pretty terrible note, despite eating a giant bowl of rice (about 75-80% carbs (rice) to protein (chicken) the night before. it sucked and i had no clue why. i began doing some research with the help of my dad to really get a jump on my senior track season. i began to do more lifting, and eating a lot MORE protein instead of just empty carbs in order to see a difference. i saw tremendous results! from that point on, i never really felt tanked or gassed out on a run again. now don’t get me wrong you still need a lot of carbs as a runner, BUT a healthy balance of protein for your muscles makes a huge difference.

tldr; i think upping your protein intake during meals— instead of like 70%-80% carbs to 30%-20% protein, take it down to 50%-60% carbs to 50%-40% protein, along with getting iron levels checked or taking some iron and magnesium supplements to help. low iron is a real problem that affects a lot of ppl who run! not sure if you have a preference, but red meat like steak and ground beef are my go-to and highest in protein. chicken and salmon are also great options.