this is killing me😩😩😩😩🤔🤔

I really wonder why my back hurts so much. I'm 25 wks, I really don't know how many pounds my baby has( many 1 ) but damn, why my back is killing me ALL THE TIME. I work 8 or 9 hours, seating in a chair in front of a computer & my back is fine but as soon as a stand up for 5 minutes the pain is  crazy. Idk if this is normal. Any advice or anyone with the same problem? 😩😩😩😩