3 Days Late

So day before AF was predicted I had a few hours of very light bright flow. My period normally starts with brown discharge then red back to brown. I only used one tampon and it completely disappeared. I don’t know if this was my period or implantation bleeding. I ovulated day 16/17 so I know it can take up to 12 days for implantation which would’ve put me at day 28. I have always had an extremely normal cycle. My cycles have been 27/28 days and I’ve ovulated the same time every month. I’ve never had a period only last a few hours (on or off birth control). At 8 dpo I had extremely sore breasts and painful nipples (never had this symptom before a period).After this “period” I’ve been nauseous and had headaches everyday. All my tests are negative. I’m feeling like I’m crazy but I have this feeling I’m pregnant and I didn’t have this other months. So now I’m 17dpo and still testing negative. I’m afraid it’s messing up my fertility predictions bc I don’t know if I count it as a period or if I’m totally out this month.