Have you been eating a balanced diet? Sometimes the symptoms you mentioned could be due to an unhealthy or incomplete diet.
What kind of work-out do you do? Do you eat during your lunch break prior to the work-out? Do you eat a heartful breakfast? Answers to these could provide clues to what is making you nauseous and faint.
Loss of electrolytes can also cause these symptoms. It would be best to drink electrolyte-repleneshing liquids, such as Gatorade, than water.
You should also have your condition assessed by a doctor. A cardiovascular condition may also present with such symptoms.
Hope this helps.
i sometimes eat breakfast but not always. i dont eat before i workout, usually after the sick feeling goes away. I workout upper body one day then lower the next and just mix it up. I am 25 5'8" and 155lbs. as far as a balanced diet i just eat whatever the wife cooks...LOL but i do drink alot of Dr.peppers (about 6 per day).
It's normal to feel bad after workout, but it sounds like you are just running out of energy way too fast. Eat breakfast, if you don't, then don't exercise during lunch. It would help to know the types of workout you do to adequately analyze your situation.
Visit a doctor to analyze your blood or just get a physical to make sure your body is in good working order.
I'm going to assume somethings, a hard workout and low food, so it could just be low blood sugar after a workout and maybe not enough cool down. I hope you stretch before working out to decrease chances of injury. Anyway, just try Gatorade instead of water next time, I hear the Rain version is easiest on the stomach.