Alamak 38 weeks dah, exciting! Honestly yang you describe sounds like Braxton Hicks contractions mixed dengan baby dropping into position, which is pretty normal at this stage, tapi since you're having pain turun ke area bawah perut and dekat belakang, better to check with your doctor or midwife just to make sure everything's good and tiada signs of early labour atau apa-apa lain yang perlu monitor. A few of my mum friends had similar experience dekat 38-39 weeks and doctor kata it's normal, tapi they still prefer peace of mind by getting checked out. Jangan tunggu lama-lama kalau rasa tak betul or kontraksi becomes more regular, sebab sudah malaun dah. Take care!