Understanding Pregnancy Dates & Early Ultrasound Findings

Question
the first day of my last period was on 19/04/06 i took a pregnancy test on 17/5/06 which came up as positive. this was confirmed on 21/05/06 by the doctor. on 31/05/06 i was taken into hospital with stomach pains and had a scan the doctor seen the yolk sac and confirmed i had cysts which could have been causing the pain, theworrying thing for me is that i thought i was about 6 weeks but according to the doctor the sac was only about 4 weeks and no heartbeat culd be seen as yet and that i have to go back in 2 weeks for another scan, this has concerned me should i be worried and is there any explaination for the confusion on dates and the scan,
thankyou
michelle

Answer
According to your dates, you should be 6 weeks pregnant at this time. Prior to 6 weeks, we only see an empty gestational sac on sonogram. After 6-7 weeks we can see  a gestational sac, a fetus, and a fetal heartbeat. Be patient and repeat the scan in two weeks.If  a pregnancy test was positive on May 17 (4 weeks from last period) it is usually accurate. You have not had any vaginal bleeding. The pain is common in early pregnancy.