How do you make your body adapt to eating earlier in the morning?

As some of you might know, I recently went from sleeping @ 5–6 am and waking up at 1 pm to sleeping @ ~11 pm and waking at 6:20 am (college starting up again does that to you). I have never had to wake up that as early as 6:20 though. And I am unable to eat my breakfast (oatmeal) before leaving for classes. I feel nauseous if I try to eat anything that early, and I just can’t stomach it. Since my classes are pretty hardcore and back to back (with only 5 min breaks in btw), eating something before leaving is important so as to stay awake and have the wheels in brain turning in said classes. Is giving it time to adjust the only solution to this problem? Or is there something else I can do so as to eat early and not feel sick?

Bonus – anyone know the scientific explanation for why this happens?