unless your periods are regular we can not take your missed period to estimate the gestational age
of the baby.
If you had not used any contraceptive
pills for 5 to 6 months before conception, or any medicines to change the cycle duration, had at least 3 regular periods before conception your date can be taken to calculate EDD.
So, at present you have to take ultrasound
wise gestational age as slandered. As in TVS also fetal pole
may not be detected in early pregnancy.
Better you go for repeat scan after 2 weeks.
Your gynecologist prescribed progesterone
to you which will help in the growth of the baby. No need to worry about side effects of that medicines.