I had a positive mammogram and sonogram after my flu shot this past October!!!!
I had the flu shot on Oct 20--on Oct 23 I had my usual every 6 months PET scan (for uterine cancer, which is stable)--got a call back that an enlarged lymph node was found under my left arm--and to go back for a mammogram and sonogram, which I did. After comparing those films to my past films, the conclusion was that the enlarged node was from the flu shot. After the flu shot I had a swollen arm for a few days--i was also black and blue--needed to use cold compresses for a few days to get the swelling down--and a steroid cream. Two months later I had a sonogram of that node and once again it showed selling. Three doctors have told me it's still from the flu shot--they've seen this happen before--and it might be a long time before the node goes back down to normal.
So where do I stand with the COVID vaccine? I don't know as I cannot get an appointment--no one in my area has any vaccines anyway--might not have to worry about this for the next few months. But when the time comes, I would get it in my right arm--not the one that had the flu shot. And so, yes, you can have an issue if you have a mammogram after a flu shot.