I Am 60 Year Old Female. I Have A Lump

I am 60 year old female. I have a lump under my right arm for about the last 3-4 weeks and it appears to be getting bigger. Is causing discomfort and soreness. I have had smaller ones before, but went away in a few days. This one seems different. I had a biopsy on left breast 6 months ago due to abnormal mammogram. Benign although I am to repeat mammogram within the month. Should I be concerned about this lump?