Details about implantation?? Need answers!?

Brownish spotting for 4 days...almost gone. Missed January period completely but hoped to catch ovulation this month. I've never been more than 2 days late except when I was pregnant for my daughter. My doctor admitted the blood test could have even missed it when I was 2 weeks late but won't retest until I miss it again this month. My period isn't due for another 4-5 days...