My period is late

I’m usually pretty regular at around a 29-31 day cycle, even with my PCOS. I take metformin to help me ovulate, and I had mid-cycle cramping this month and we BD’d like crazy in the fertile window. Now I’m a few days late, with no sign of AF on the way (usually I’m cramping like crazy and spotting right before). I have had headaches almost every day for the last week. I took two pregnancy tests yesterday, one First Response Early Result and a 88 cent cheapie from Walmart, and both were negative, not even a faint line... I feel like I’m going crazy waiting for my period but still have no cramps. Could it be a false negative? I have read online that that is common with PCOS.