I’m sorry, I really don’t know for sure what may be the cause of the ‘popping’ sensation you describe. I can only guess that maybe mucus from your cervix is collecting around the neck of your womb. The cervix joins the vagina at an angle, creating a ‘blind corner’ in which fluid may collect when you are lying or sitting. Maybe when you move, the loose folds of your vagina are then opening slightly to release the fluid – thus creating the popping feeling. Alternatively, although your baby’s head is not yet engaged, it’s normal to feel increasing pressure during these last weeks of pregnancy. Don’t forget that your muscles are probably not so toned during this pregnancy as they were in past pregnancies. Tell your midwife, or phone the maternity unit, if you think that your waters have broken. Many women find that they lose more mucus during late pregnancy and sometimes this can make you feel quite damp between your legs. If you’re in doubt as to what is happening, wear a thin sanitary pad (preferably not a super-absorbent one). If your waters have broken, this will quickly become wet. I’m sorry I cannot give you a more specific answer. If you’re still worried, do phone your midwife.