Ovulation question

Amy

Last Wednesday I had to have an shg. While doing the ultrasound, she asked me what day I usually ovulate on. Normally it’s around 17 to 19. This was day 10. She said I had a follicle that was 10mm so she didn’t think it would be any time soon. Well, that Saturday I started getting my symptoms of ovulation. Which would be day 13. Can a person ovulate with that small of a follicle or can they grow really fast?