I Was Meant To Get My Period On The 27/12

I was meant to get my period on the 27/12 but didn't get them until 1/01, my period is always regular and never that late. I last had unprotected sex on the 19/12 so I took a pregnancy test first on the 28/12 then on the 31/12 then today 6/01 and they have all come up negative, I've also had a blood test done on the 29/12 which also came back negative. My period is nothing like every normal period that I've had in my life, I normally get heavy periods and strong period pain, there hasn't been a time where I haven't had period pain on my period so this was unusual. So when it started on 1/01 it was bright red and not heavy at all that I didn't need to change my pad. I only had one pain that lasted two minutes and that's all I've gotten. On the 3/01 it went very very light to a dark brown colour then on the 4/01 day it went to a light pink colour then on the 5/01 it went back to dark brown then today it is just light brown discharge. Basically what I want to know is there a chance that I am pregnant and that this could possibly implantation bleeding? I have on 3 year old child so my partner and I have been trying for 5 months now. I have also been experiencing nausea, fatigue, headaches, turned off foods, weird cravings, itchy nipples.