Suggest Treatment For Numbness In My Arm

I have been having an odd feeling sort of like numbness in my left underarm, and sometimes I get pains in my left breast. I am 45 and have mamagrams regularly althoug I have not had one this year. I also have had anxiety attacks that have led me to the emergency room and they test for heart problems but both have come back negative. I dont want to get scared but this feeling is annoying. What could be causing it?