Why do I gag and get sick whenever I get excited or nervous?

I have done this since as long as I can remember. I am 16 and a male. It seems whenever I get very excited about something, or get nervous, I get sick to my stomach and gag. Sometimes It is not too bad, but other times I can't even walk or move. Like I said, I have done this for as long as I can remember. I have tried everything to get it to stop, like antacids and trying to forget about it. Only thing that I can seem to do to calm my stomach just a little is sip water slow.

I don't know anyone else that has this problem. No one understands this. It absolutely sucks. It is really messing up my life. Now that i have to take my driver's ed road test soon, I don't know what to do because I know that I will be nervous. Don't get me wrong, I am a great driver. I have drove before when I was like this and it involves one hand on the wheel and the other with a bottle of water. In fact I drive better with one hand...but I gotta have both hands on the wheel for my test. I don't know what to do? Can someone help me? thanks