i too became concerned two days ago I noticed an indentation under my left breast, verynoticible, no pain, can't feel a lump. Went to GP today and she said she can feel a hardness and the dent is noticeable but it could just be hormonal.
last year I had a recall from a mammogram for my right breast as they had noticed something, turned out it was calcium deposits. Left breast apparently fine. Anyway have been given an urgent referral tomorrow at local hospital, so am expecting, mammograms and biopsy, dreading doing it again but got to face it and if it's anything I will have caught it early. Hopefully. Feel sick to bottom of my stomach but trying to remain positive.
Anxiety is fairly inevitable when waiting for appointments, but you've done what you need to in getting it checked out, so just try & distract yourself & carry on as normal until the appointment.
It's absolutely right your dr has referred you for ultrasound, as any breast change must be properly checked out.
As your dr says, chances are, all will be fine, it mostly is.