Try to sit straight po para hindi masakit sa likod. As your tummy grows, medyo pabukaka na talaga pag uupo, pero ok lang para comfy and hindi maipit ang tyan. Wag din po cross legs kasi it can affect your blood circulation, cause swollen ankles, or varicose veins.
Here's a full article po:
https://parenting.firstcry.com/articles/best-standing-sitting-positions-during-pregnancy/
Jonalyn O. Pasulot