Need opinion please!

[girlgirl4422]

Hello, so I am very confused about the whole timing of ovulation, implantation bleeding, and early pregnancy symptons. I have been on the pill for four months before stopping. My periods were pretty much regular throughout this whole time. I got my period from nov.27th-Dec 1st and it was like a typical period. I had unprotected sex the 2nd, 3rd, and 4th of December. Yesterday on the 16th of december I noticed I had very light pink spotting for less than an hour but not enough to even use a tampon or pad. I am having mild cramping and aches in my back. I also am experiencing diarehha occassionally. This is pretty uncommon for me to experience spotting since I never had. I was wondering if this could be signs of implantation bleeding and cramping? I know sperm can live up to 5 days in the body but I was still unsure when i was due to ovulate. Could these symptons be ovulation? or signs of implantation? I am very confused. Also, I took a pregnancy test today on the 17th of december but it was negative. And it was very early for me to take a test so I cam skeptical of the results. Any input or advice would be very much appreciated! Thank you!!