Late ovulation

Hi ladies!

Having a rough day today . According to my lmp I should be 6 weeks today. Had an ultrasound today and they couldn’t even detect pregnancy .. hcg is good so don’t know what’s going on.. I always write down when I have intercourse so I’m sure I’m less than 6 weeks. Doctor still didn’t take that into consideration .. im really frustrated .. is it possible i ovulated an entire week later? Anyone out there had this happen?