Getting sick after a workout

I need more facts to help. What is your workout like? What are you eating before the gym?Do you drink milk or eat milk products before workouts? I ask because that lactose in milk can easily make you puke if you go running. Also, milk takes a bit for the body to digest. If this is the case eat that stuff after your workout.
It is possible to over-hydrate, but it is fairly unlikely given that you need to replace water lost by sweating. I also wonder if this is due to an electrolyte imbalance. In short, both sugar and sodium are needed by the body to function. Sweat robs the body of water and salts so they need to be replaced. This is why Gatorade is so popular for athletes because it replaces both. However, you don't need it and it has a good amount of calories.
Feel free to respond if you want any more help.

I had the same problem and for me it was food...if I ate within three hours, it was coming up. I'm an early morning exerciser so I solved the problem by getting up, having a quick cup of coffee and hitting the weights. No problems since
Might just be your body talking...

Yeah, delay your food... I can't eat within 3 hours of working out, or I *will* hurl. I can eat something very small on weekends when I go work out first thing, but more than half a banana? Yep. Water doesn't have any affect.

Though, I will say, there are times when even then, I push it too far and have had to pull over on the way home. That's a proud day.