HUGS! You could have Oed later or maybe implantation took longer. Our bodies are regular until they aren't. I used the Free Menstrual Calendar to track my periods since 2009. I was 28 days, O day 14 since I was in 6th grade until last year when I got a cyst and BAM had a 60+ day cycle, then a 50+ day cycle, then my cycles ranged from 20-36 days for a while, and now they seem to have regulated to a 30 day cycle. Our bodies do weird things.
Is your doctor running blood HCG tests? I would highly recommend doing that, do one 2-3 days later, and one more 2-3 days later. I was pregnant when I got the cyst and my first scan at 6 weeks there was NOTHING. No sac, nothing. So my doctor had me doing blood HCG tests every two days for a week to make sure my levels were doubling and scheduled me for another scan a week later. Turned out, I had my dates wrong and wasn't as far along as I thought. Ultimately, I made the choice to not continue the pregnancy because my cyst was so huge the danger of losing the ovary was too high. It was really difficult at the time, but yeah. Point is. Get some bloodwork done and stay positive.