Just a suggestion: You are more likely to get answers if you start a new thread of your own with your question. People often overlook a question tacked on to the end of old thread, because they tend to assume it is just an additional reply to the original poster.
I have had a burning sensation under my left arm and down through my nipple for nearly 2 1/2 years. This happens about twice a year and lasts for 1 to 3 months each episode. I have seen my doctor and OB/GYN. I have had mammograms, ultra sounds, CT Scan, xrays and they cannot find the cause. I have also had a fitting for support bras. Since they can find no cause, they relate it to stress. I don't really believe this as the episodes do not correlate to any particular stressful periods in my life. If anyone has an answer , I would like to hear it. Thanks.
Sorry but I am not a doctor but I know how what I have read in the enclosed link.
While you wait for a doctor's answer you could read the enclosed link with information from the Mayo Clinic.
http://www.ehow.com/about_5154831_causes-burning-sensation-breast-tissue.html
Now don't freak out, read it patiently and wait for the online doctor or someone who knows about these issues.
Take care.