Your doing all of those exercises 3 times a week, plus not eating enough, and on top of it all not resting enough? I think thats the answer. Diet and rest are so important IMO. Try to up the meals, and sleep for a week, see where you stand at that point, I'm sure that will be the solution.

If you think the heat is gettin to you definatly be sure to drink something during your workout. Like eric suggested gatorade, or maybe try some citulline malate.