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.
Now don't freak out, read it patiently and wait for the online doctor or someone who knows about these issues.
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.
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.