I am older than you are but was called back for a diagnostic mammogram. I went in a bit early and requested to go straight to sonogram. The lady at the front told me that wasn’t protocol. I told her I understood but it was my body and I was respectfully requesting to go straight to sonogram. She said I would have to discuss with the doctor and I said I welcomed the opportunity. They sent me back to sonogram and it was no problem (and the doc never saw me to discuss).
I knew if the abnormality was present in the diagnostic mammogram the next step was sonogram. They determine from sonogram if a biopsy is indicated. My thought was why expose myself to more radiation when the sonogram is a more definitive test.
I also know from working in the medical field that protocol can sometimes be determined by insurance. Meaning your insurance may not pay for a sonogram without a secondary mammogram.
Regarding nursing, I would contact a lactation consultant and ask their opinion about your milk.
Being nervous is to be expected. Hoping everything is resolved soon for you.