Good day everyone! I'm at 31 weeks and have started experiencing dull pain…

Good day everyone! I'm at 31 weeks and have started experiencing dull pain in my lower abdomen and pubic area. My bones feel like they're cracking after sitting down or getting up. Has anyone experienced this? Is it normal? I think I should get 3 ultrasounds but I'm afraid it might be harmful for the baby. What should I do? ?