Ay alam ko yan, mama! That's super common sa late pregnancy, yung baby ay mabigat na talaga and sitting for long periods just puts so much pressure sa area na yan, plus your ligaments are all loosening up na to prepare for birth. Try to get up and walk around every 30 minutes or so, and a pregnancy pillow or cushion with memory foam really helps when you need to sit, a few of us mums swear na ginawa nito mas bearable ang last weeks namin. But since you're almost there at may significant pain na, best to mention it sa OB mo on your next visit para sure lang walang other concerns, okay?