Preg or not preg

So I guess I started my period, but it's very light. This is the same way it happened last year when i found out I was pregnant. I guess if i miss my next periodi will check. I was 1 1/2 days late on this one, but majority of it is just spotting.

I have a question 🤔 so if what it looks like ( implantation bleeding ) how would I know? And when would it have happened. The bleeding was on the 18th, Sunday. Adding my glow calendar, I keep track of everything, and on the 18th I noticed it after sex. But my period should start this week. I'm no expert at this either. I've gone to the doctor recently july 25 and had a pregnancy test, but was negative would that have been too early? Like how long does it take for implantation bleeding to happen? I had it happen my first pregnancy and i was pregnant. Yes i know my screen shot was taken the day of but i didnt get great answers somewhere else.