No, it is not dumb. What would be dumb is that you think you can get a definate answer here, and obviously you know you have to go to the doc. Good for you!!!!
If you are very irregular, this could well be a period for you. Remember that many periods have the same or similar side effects as pregnancy.
You ask what the chances of having your period while pregnant. Well, actually the chances are pretty high, it happens to quite a few women actually. Also, please read
this thread about the withdrawal method.
Maybe while you are waiting for your doctors appointment you should take a HPT and be sure to use first morning urine no matter what the directions say.