Cycle day 40

So according to my calendar, my last menstrual cycle started March 1st.. I have a 24-28 day cycle so I was supposed to start March 25th.. cycle no where to be found and glow is saying 16 days late.. haven’t had sex since last year so I know I’m not pregnant.. I’m neverrrrr late.. I’m really early some months but late? NEVER.. obgyn in my network can’t see me until June first because they’re booked so far out. Which is causing me to panic so bad because what if something is really wrong and they didn’t catch it in time?!?! Now I’m wondering if I’ll get a cycle again.. I’m 39.. anyone cycle was late and they turned out fine?! What was the reasons