Eh normal je tu sayang, most of us mummies experience this dekat third trimester, perut dah besar, baby pressing down, ligaments stretching, so duduk lama memang tension kat abdomen. A few of my mum friends complained about the same thing around 36 weeks, especially kalau duduk dalam position yang sama untuk lama, so try to change position every 30 mins, maybe lean back with a pillow or stand up and walk around sikit. But just to be safe, check with your doctor or midwife next appointment to make sure it's just stretching pain and not something else, especially since you're getting closer to delivery date!