Lump the size of a small cantalope, what is it?

I have an enormous lump in my right on the inner left side. It has been there for approx. 1 1/2 years and started out the size of a marble and has grown to this size in the last 9 months. i am 53 years old and have had a complete hysterectomy when I was 35. I have never taken any HRT at all. Up until the last month this lump hasn't bothered me but, now it has become so large that it is pulling my skin and making irritation also. I have searched everywhere for answers as to what this could be, cyst, tumor, cancer? I have found nothing to compare my symptoms to. Does anyone have any ideas? I am going to the doc in two days but, I am scared to death. Please help!!