I am 19+4 weeks pregnant and i had my anatomy ultrasound today. babys heartbeat is normal but its measuring 2 weeks behind. i am really worried and concerned, is this normal and what are the causes for it?

The estimated size of a pregnancy in "weeks/days" is often not accurate, as ovulation may have not occurred at the exact time the dates were estimated, which will make an ultrasound not precisely the same as the dates estimated by one's last menstrual period. A repeat ultrasound in a few weeks may show good interval growth of the fetus. Ask your OB physician for guidance.