Hey mama, ang tightening na yan ay Braxton Hicks contractions, super normal especially na malapit ka na sa due date, a few of us nag-experience din yan around 37-38 weeks and honestly it's your body's way na nag-practice na para sa actual labor! Since may slight pain ka and it's affecting your movement, definitely mention it sa OB mo on January 4 kaya lang para ma-check if these are just practice contractions or if something else is going on, plus pwede niya i-clarify din which EDD ang mas accurate (usually ang second ultrasound is more reliable but your doc will know best). In the meantime, try to rest when you feel the tightening, hydrate well, at kung sobrang sakit or may bleeding, go to the ER na agad, better safe than sorry when you're this far along! Kaya mo yan, mama, almost there na!