CD 36 BFN no AF

So, I have had a regular cycle since I started my period at 11 years old. Never missed a period and in the last 3 years of tracking my longest cycle ever has been 31 days. This cycle I am at 36 days and still getting BFN test. I just turned 40 this year. Has anyone else experienced this and gotten a BFP later than cd 36? Unfortunately, I wasn't tracking ovulation this month as we decided to take a break for a couple months. I have a doctor's appointment Wednesday with my fertility specialist but this is making me crazy! Anyone else in the same boat? Could this be perimenopause starting? I have some symptoms but it's so hard to tell the difference between pms and pregnancy. Any encouragement...late bfp stories or advice is appreciated!