What Causes Big Red Bump On Right Side Of Breast?

Hi. I have this big red bump on the right side of my breast, located close to the crease of my breast. I thought I could burst it, and the big would go away. However, just the opposite. The bump is raw and sore. I have had the bump for about two months. However, I notice it is getting larger this month. I contributed the outburst to it being "that time of the month." Should I be worried.