How do I get rid of fatigue if I'm told I can't have caffeine? how must I stay awake?

I need to stay up (probably all night, yet I'm sleepy now and it's only afternoon!) because I have lots to do for tomorrow, but today I was told that I can't have any caffeine or acidic food or spice because I have gastritis. I don't want the pain to become worse. A symptom of the gastritis is also fatigue, apparently, but I need energy.