What is happening to meeee???

I O'd cycle day 22 (based on LH testing), had sex multiple times within the fertile window. My period timing is always irregular but flow is always the same -- very heavy flow the first day with painful cramping and tails off after a few days, usually lasting around 5-7 days. However this time, on CD 36 my period began light and stayed light, turning into nothing but spotting for a few days. Not once did I fill a tampon. I didn't even have any cramping! The blood itself was mostly brown which was strange as well, just hints of red and no clotting. So naturally, since we're TTC, I took a HPT and it came back negative. I figured I tested too soon assuming what I experienced was IB. But I tested again today, 1 week after spotting began and 4 days after spotting finished, and BFN.

Am I still testing too early? Was this just AF? Anyone have a similar experience? I'm struggling here!!