What Causes Hard And Painful Boil In Arm Pits?

I developed what I thought was a boil under my right arm pit but then the vein became hard and painful and feels raised for about four inches from my armpit down my arm. I have not been sleeping well and currently take HRT, but havent been unwell as such (apart from tired). I went to the doctors and he prescribed "Hirudoid" cream and has made an appointment for two weeks time to have some blood tests and is possibly referring me to the hospital. I now have the same feeling in my left armpit, should I go back to my doctors? I dont want him to think I am over-reacting, but I am starting to worry