Lump in armpit and other symptoms

I am 31, no children, non-smoker, no other health issues and no history of cancer. In October, I noticed something strange on my left breast. It really stood out, like a strange puckering just above the nipple, where the skin suddenly became raised and slightly discoloured in a noticeable way. This went away after about a week, and I decided it must have been the result of a blemish or something.

About a week later, I noticed a lump in my left armpit. It was slightly tender to touch. I also noticed that my left breast now appeared to be just a tiny bit larger than my right, something I had never noticed in my life before, almost like it was swollen. There has also been consistent, but quite mild, pain in my ribs on the left side. Fast forward four months later, and the lump in the left armpit is still there, and the left breast still seems slightly bigger.

I can't see the lump with my eyes, but I can feel it to touch. Today I was able to actually grip it and it is firm and oddly shaped, almost like a flat olive. It is slightly painful when touched, but nothing extreme. I compared it to the other side and the other side has nothing like it, it's just normal on the right side. I have made a doctor's appointment for next week. Does anything I've written sound familiar to anyone? I'm confused and a bit worried as to what it could be, mainly as it has been around for four months and hasn't gone away. Sometimes it seems to swell up as well, and be bigger, but it never goes away.