What Causes Pain And Burning In The Armpits And Upper Chest?

Hi for the last 9 - 10 months i have had pain and burning in the armpits and in the upper chest under the armpit. The pain can be a bad ache to a sharp pain and burning.At the moment my doctor has prescribed gabapentin as he thinks its nerve pain but its not really working. Please i am desperate for a cure to this as it is ruling my life. Apart from this i am a healthy if a little over weight, 36 yr old female... Please help......