2 positive home pregnant tests. Had transvaginal ultrasound 16 days post ovulation. No sac seen. Is this normal for 16 days after conception?

Too early. It is unusual to see a pregnancy on ultrasound until about 5 weeks, which when you are a week late. If you ovulated late, it could show up any later. If your or your doctor is concerned about an ectopic pregnancy it should be repeated.