Breast tenderness

I need advice, so I had a “period” for 3 days which was a darker pink and brown. I didn’t think anything of it, then I noticed a few days after my breast are still sore, 11 days later my breast are STILL sore and hurt along with my nipples , so what could this be? I also keep having pressure when I try to use the restroom, and having mini cramps in my left side. I took a test but shows negative ? Should I go get a blood test done ?