Re: Tips to increase energy and endurance?
I have vague memories of being a grad student AND part of the varsity rowing team. That meant on the water at 5:30 AM during the week, weights and/or running in the afternoons, and training/competitions on the weekends. Couple that with occasional lectures, lab time, library research (twas before the internet), and I walked a thin line of just barely not breaking down. Sometimes I actually did break down and get sick. Not for the faint of heart.
International competitive athletes are full-time athletes. You're nearly training full-time.
You need to keep food and fluid coming in DURING training. If your dojo is "old school" and won't let you either rehydrate or nibble on something during occasional breaks, you're going to wear out. On the other hand - if your training is "normal working pace" - it's possible to do it all day - our forefathers rose at dawn, farmed (for example) all day and went to bed at night having put in 10 or more hours a day of physical - continuous - but low-intensity work. Pitch hay bales for 10 hours/day for a week or so - eat LOTS of food.
I think, from your description, the big shortcomings are food and rest. You need to eat a well-rounded "diet" and to nibble all day so you're not getting depleted while training. In competitive sport, after a big hard endurance training session, we try to get athletes to have a "recovery" snack (e.g., a fruit smoothie with protein powder added, or a ham and tomato sandwich) within 15-20 minutes of finishing training - according to our nutrition consultants, the muscles are "primed" to store glycogen during this period - shortly after training - and that will help you keep from breaking down, too.