Implantation Bleeding or Body Changing

New to "madeformums" I'm not sure if I am experiencing implantation bleeding, 11 days before my periods were due I had red blood on my tissue after wiping. I looked at my cycle calander and the dates added up for implantation. Since then I have experienced a slight pink colour on a few occasions when wiping but not every time, my periods are due in 4 days and I am like clock work, I have never experienced a period warning 11 days before due date, I usually do the morning before they arrive. I got alarmed as my breast are so sore, veiny and a size bigger. I have never been so tired. My partner and I have been using the withdrawal mechanisim for almost 4 years. We are not trying to conceive however we are not using contraception. I just turned 40!!! Is it my body changing or could I be pregnant. I'd really appreciate your input.