Hallow Dear,
The calendar method calculates the period of gestation from the date of last menstrual period (LMP). Actually, the conception takes place about 2 weeks after LMP.
Ultrasonography scanning measures the length of the embryo to assess the age of gestation. Hence, in early stages of
pregnancy, a lag of 2 weeks between calendar calculations and scan assessment may be observed.
Probably, 5 weeks is too early to appreciate the foetal heart activity. Please wait for a week to 10 days more and then get another scan done. If even then the foetal heart activity is not noted and the baby is not growing, it may suggest non-viable baby. In such event, you may have to terminate the pregnancy.
Since you are having some amount of spotting, till the status of baby is ascertained, please take some Progestational preparation with the advice of your Obstetrician to stabilize the pregnancy. If the baby is viable and if the baby's heart activity is noted, you may continue the Progestational preparation with the advice of your Obstetrician.
I hope this will help you.
Dr. Nishikant Shrotri