I was scheduled for a routine mammogram until I mentioned a small lump in armpit. My PCP automatically changed the prescription to diagnostic mammogram plus ultrasound. The underarm lump was nothing but the two tests confirmed a small tumor in left breast. I had lumpectomy and clear sentinel node biopsies. My follow-up instructions from oncologist for the next five years include physical exam and blood work, including tumor markers, every six months and yearly mammogram plus ultrasound.

Maybe you can lobby for the ultrasound or get a second opinion. Maybe change doctors. I'd want every reasonable test that can be done especially if it's non-invasive and pretty risk-free.