Implantation and BBT

So AF if supposed to stay today. I haven’t seen anything all day until just a moment ago I had a SMALL about of brownish spotting. According to Glow I’m 12DPO. Would it be too late for implantation bleeding? Also today was the first day that I had a big drop on my temp. all week...it’s been very high all week...compared to normal. Just trying to figure out how to read what my body is doing. I took a PT 2 days ago and got a BFN. Took another today and got a BFN too... Praying for baby #1 and knowing that God is SO good in the meantime! Any help would be appreciated.