Dizzyness and the diet

I haven't counted calories, but I would think that I am taking in between 1700 - 2000 per day.  I eat a high protein breakfast and small snack a healthy lunch another small snack, dinner, and possibly another small snack.  All told, the meals are relatively small and the snacks usually consist of an apple or a 1/4c of nuts and seeds, but the the overall intake should be pretty close to my target calorie level and yet I have been feeling dizzy during workouts and struggling with my energy level.  I am not saying I feel tired all day, in fact, I have plenty of energy throughout the day, but at the 10-12 minute mark of a 15-20 minute workout I am spent.  Totally gassed.  Having trouble breathing, not sweating a lot, feeling dizzy, and definately short of breath.  A day off of exercise and a few more calories and we will see where it leads me.  Overall, staying the course.