Should I buy another brand?

Anyone got a false NEGATIVE with this brand?

I am so confused. I was suppose to start my cycle on Thursday. I had ONE spot of dark brownish blood (about the size of an eraser) Thursday night and I’ve literally had nothing since. It’s Sunday night!! This was negative. I’m wondering if I should go get a FRER? Or just wait it out?

TTC for 3 years. I am suppose to start <a href="https://glowing.com/glow-fertility-program">IUI</a> with my next cycle.