Well, I hate to pry, but why are you throwing up? If something is causing you to throw up regularly, you really need to consult a doctor. Vomiting tends to drain you of fluids and electrolytes, not to mention depriving you of any nutrition that might've been derived from what was in your stomach. It's also just very strenuous - it takes a lot of muscle power to push things out of your body. So, I'd guess what you're feeling is a mixture of exhaustion and dehydration. If you're vomiting regularly, then malnourishment may have something to do with it too.
After you throw up, make sure to drink lots of fluids; water is good, but you also lose various soluable minerals and electrolytes that make up your digestive fluids, so something with sodium and potassium (like Gatorade or other sports drinks) is much better. If that isn't handy, try a multivitamin or some bananas with plenty of water - if you can stomach them. Don't force yourself to eat much until your stomach has settled; one of the worst things you can do for chronic nausea is to keep putting things back in when you can't keep them down.
Take care,
~Joe