Hi Krista, welcome! Sorry you are going through this scare right now. About 80% of breast lumps are benign. Lumps can be solid (tumor) or fluid filled (cyst). Most cysts are benign, and most tumors are benign, called a fibroadenoma. There are a few other benign conditions too, and cancer is one of the least likely situations. You are right, family history has little bearing. Having a history in the family might make you more sucesptible, but regardless, it is most important to check out.
A mammogram is an x-ray. They will position your breast between two (cold) plates, and they will manipulate and move you to be just right. Then they will apply compression and your eyes will widen, you will say ouch, and then it is over. It is momentarily uncomfortable.
Mammograms are standard as first line in trying to diagnose a problem. Some things are not visible on a mammogram, either due to dense breast tissue, shadows, or for an unknown reason it is not picked up. Don't freak if they need to do a repeat picture..it does not necessarily mean they found something, but often there is movement and they need a clear shot.
Ultrasound is painless. They will rub jelly on your breast and run the wand over the area and take pictures on the screen. The ultrasound can help determine if it is solid or fluid filled, can help locate the location in the breast...in my case, at age 30, my tumor was not picked up on the mammogram but was plainly visible on the u/s.
Lumpy breasts are common. Have you felt these before? Most likely it is nothing, but please don't let anyone brush you off telling you that you are too young or not at risk. If you are a woman, you are at risk. Best to just get it checked out. I would also recommend that you obtain copies of the radiology reports for your own records.