I completely understand how you feel--it's definitely scary to even hear it mentioned. But as Squibbles said, if it were to be the case for you, there are several medicines, and there's more research and more research being done to get us closer to understanding it! Some people have it, and have almost no symptoms, so don't think the worst.
As far as whether doctors are always right about it--not always. You should get a copy of your test results, and get a second opinion, if your doctor does say he or she thinks it's MS.
Hang in there Sophie--there are many knowledgeable people on this forum who can give you some great advice. And we all understand how you feel!