When people feel occasionally sick after eating, they may throw up or try to, to rid their body of the harmful food. It's not forceful, but more like a "get me to the bathroom or I'll spew all over you."
If you're doing it all the time, and you can control when you throw it up (like you can make it to the bathroom and stick your finger down your throat to make yourself throw it up) then it's something deeper. It could be in your head. It could be an eating disorder. If that's the case, you would need to talk to a *psychologist* about WHY you're doing that.
Bulimia is a psychological disorder and there are many underlying issues in relation to this disease. It's not about merely losing the weight. There are some insecurity and control issues. Sometimes it's triggered by an abusive person, let's say. May not have anything directly to do with eating and weight.
How would you describe this "sick"?? Physical pain in your body? An overwhelming feeling in your head?
Take note of when this happens. Every meal? If it's every meal, it's most likely in your head, I would think. Unless you're a very unusual case of someone being allergic to everything or something. If it's only some meals, figure out if it's something you're eating. Perhaps you're eating tomatoes every time you throw up, then you could try to have a tomato free diet and see if it works.
Hope that helps.
Sounds like Bulimia to me.