An ultrasound or a mammogram? I don't know what to tell you, except if your doctor doesn't think it is cancer, it probably is not. Good luck, if it's really making you crazy, you could see if you can get in sooner.
I have had cysts in my breasts that had to be drained. They performed an ultrasound to identify them and then the doctor stuck a realy small needle in and sucked out all the stuff from the cysts. It didn't hurt.
Doctors are pretty good at knowing the difference when they examine you but the ultrasound will reveal a lot. I was told that in younger women mammograms aren't so effective because the breast tissues are too dense. That's why they use ultrasound, it's a better tool for younger breasts apparently.
I know that saying try not to worry is easy but doing it is almost impossible when your faced with something like this for the first time. If you can make some phonecalls perhaps you can get a quicker appointment. The squeaky door gets the oil.
Best of luck.