How do I figure out how far along I am?

Marie

My LMP was on July 11, and I ovulated on CD 16 (July 26) or CD 17 (July 27). How can I figure out how far along I am and my true due date before going to the doctor? My app says 6 weeks 6 days but I don’t think that’s correct. I think that’s going off if I ovulated on CD 12 like majority people do. I went on Wednesday to the doctor but she thinks I am earlier than she expected because we only saw the yolk sac. I go again this coming Wednesday.