Implantation or start of AF?

I ovulated between 2/14-2/18. I had unprotected sex with my partner. Due for my period 03/01. I’ve been experiencing PMS/pregnancy symptoms starting last Wednesday, my boobs have been super sore and feeling heavier than normal, nausea, extreme fatigue, etc. I started testing earlier this week because you can “test early” all negative. I took one yesterday 2/26 and I thought I saw a super faint line, but chalked it up to an evap line even though it appeared within the time frame. Took one tonight, and I thought I saw another faint line, but just ignored it and assumed it was negative. I’ve been having mild cramping peeing more often the last couple of days, and then tonight, I went to the bathroom because it’s been feeling like I’m gonna start. I peed, and wiped and it was a very light brown mucous string on the toilet paper. Nothing. Picture attached.. is this possible implantation spotting/bleeding or possibly just the start of my period?

Thanks in advance!