Two wks late positive test no sac on ultrasound

Lisa

Lmp was 12/16 ovulated late 1/7- on 1/13 and 1/16 negative tests then 1/21 positive. Went to ob thinking I was around 6 weeks when they did the sonogram all it showed was a thickened endometrium which she said looks like early stage of pregnancy no sac . I’ve had a chemical pregnancy in the past so I worry this is happening again. Going for bw tom to see what my levels are . Anyone else experience this?