Dear golster - sorry for the delay. I just read your question and hopefully this answer will bring you some comfort.
I had the very same problem for many years:
Left breast pain that seems to connect with pain in left shoulder and elbow. It was so unusual for me to connect the two, that for a long time I was thinking I have some weird rheumatic pain (no swelling) that comes and goes regardless of weather. I even took arthritis med, that actually seemed to work.
Since November I had a scare with a mamm that I had to redo, followed by diagnostic mamm and US at the left breast. A 10mm mass was found, that I could actually feel, but thought it was a cyst, since I had one before in the same breast. Since there was no cyst found by US and mamm, just calcification and a mass that seamed connected to a lymph node(?), I had a biopsy done by the surgeon (=benign)and will have a follow up mamm in 6 mo, because the lump (1 cm) did not disappeared, and my breasts are extremely dense.
Since then I am keeping a record of the time when the arm/elbow pain appears and how it is connected with the breast pain (in the region of that lump). The surgeon also did not pay much attention to this concern, but my family doctor told me it might be due to hormonal fluctuations, and he will run some tests in the near future - do not know exactly what type of tests because I will have the appt. in March.
Hopefully this helps.
All the best - DCM
Dear golster: Without evaluation, including review of the mammogram, ultrasound and clinical breast examination, it is not possible for us to speculate on the cause of the arm pain or heaviness in the breast. Although the mammogram and ultrasound, by your report, are negative, you mentioned that your doctor felt a lump. In a general, if there is a lump that can be felt, further evaluation is necessary. It may be that your doctor feels that this lump should be evaluated by a surgeon to determine what it is. Hopefully, your discussion with the surgeon will answer some of your questions.