I'm really confused and worried.

My temp usually drops right before ovulation, and also the day I start AF. My temp the last 4 days has been significantly dropping. I've Googled it and can't find any info other than people suggesting ovulation. However I've been taking OPKS every 3 hours and they're all negative. I temp vaginally so it's not because my mouth is open. I don't sleep in the cold. I temp at the same time every day. And my thermometer isn't broken. Please help.