Aw mama, kaya mo yan! Honestly those cramps at back pain sounds promising na, a few of us here got into active labor with similar signs kahit walang mucus plug yet, kaya hindi yan required pa. Try walking around (the hospital grounds or even just around your house), change positions frequently, maybe squat or use a birthing ball if you have one, dahil gravity really helps bring baby down, one of my mum friends swears the ball and walking combo worked wonders for her. Pero since you're already 39 weeks and the pains are on-and-off, definitely call your OB na para ma-check mo if you're dilating, basta sure kami na you're in good hands. Kaya mo ito, mama, soon na makikita mo na si baby!