Hi karilyn, welcome!
As for the ultrasound, they may do it anyway. With the u/s, they can tell if is solid or fluid filled, but they can see other characteristics of it. In my case, the mammo (I was 30) showed nothing, but the u/s was clearly showing a malignancy. They look for density patterns, borders, and they can tell size, location, etc. It can give them good information that may guide them in how to proceed, in terms of what kind of biopsy they use.
Even though it is the same area as was looked at a couple years ago, it may be a new issue. And it may be good if it has not changed much over time.
At any rate, stick with us and we'll support you through this. We'll be waitng to celebrate with they give you good news!