Pain and lump in the breast and armpit

I am 28 years old (never been pregnant)and about three weeks ago I felt a lump in my left breast (which is bigger in size compared with the right one). I went to the doctor, after the examination, he said it is a fiber cyst. The following days (after the examination), I felt an intense pain, and it remained for days(maybe, because the doctor touched for the examining), the lump was also firmer (before that, it was movable and liquid), I went to another doctor, he examined and sent me to an ultra sound examination. It said it was fibroadenoma.
The doctor affirmed the result. I had the pain for a couple of days but it was decreased. However, with my period, it came again. Today's the third day of my period and I am feeling the pain and I can also feel a firm thing in my armpit and even my arm hurts. I'm worried…
Thanks for your help.