I can't really say anything else that hasn't been said on this thread - but take care and remember there are some good doctors out there who actually give a damm about how you feel. Be confident that through this site you probably are a lot more informed than a lot of people so you can kick that doctors ass if he starts talking rubbish. I'm sure the tests will be fine - you'll probably feel worse if you just wait and worry. Us IBSers are tough chicks and I'm sure everyone here will give you as much support and advice as they can.
Look after yourself - at least you are doing something about the situation, which puts you in control, not your stomach.