Help! Irregular cycle and TTC

Megan

My typical cycle is usually around 18 days long. I am on cycle day 26 currently (the longest it’s ever been) and no sign of AF. I have been so tired and have had a milky white CM. But I have taken a pregnancy test and negative. Because of my irregular cycles I’m not sure how to gage when I should count a “missed period.” I don’t know if stress has caused the delay or if there’s still a chance I could be pregnant. Has this happened to anyone else??