Generally in the first pregnancy
abdominal muscles have good tone ,so it takes time to relax the muscle and showing of belly bump.it will be seen clearly after 16 wks.
U will gain wait.wait and have patience
Generally during first trimester people tend to eat less due to nausea vomiting
etc and tend to gain less weight.but when pregnancy advances your diet will improve and u will gain weight too.
Also if ur heigh is more than 5.6 feet belly bump takes time to show.
So jus have patience ,
Maintain ur diet.
Regularly visit ur gynaec.
Take healthy diet rich in nutrients .take medications properly
Hope to hear from u soon.