What Is The Small Hard Lump In Breast With Pain And Swelling?

Hi, I am a 23 year old female. For the past four months I have some noticed changes in my left breast, swelling, pain on palpation, a small hard lump, mild itching and sometimes flatter nipples compared to right breast. Most these changes flactuate with my mentrual cycle, but the lump tends to stay there no matter what. I have a GP appointment booked next week, just wondering whether I should be concerned.