when carrying very low, how do you know when LO has dropped?

jamie

I've been told at an Ultra sound I'm carrying very low. this was around 16 weeks along.... ever since I was In my 20+ week range I noticed pressure on my bladder, peeing frequently throughout the day and night and experience early pelvic pain if I'm on my feet for too long. (so sore I could hardly walk) so I've been taking it easy and basically being a couch potato lol. I'm 30 weeks now, so how do I know if the baby dropped? I had a weak cervix with my previous pregnancy, but so far my last ultrasound scan at 23 weeks shown my cervix was still long and they weren't concerned so I didn't have another ultrasound since. does carrying low cause early labour and water breaking? hence being a second pregnancy? Just because I was at risk for preterm labour with my first pregnancy, I have a gut feeling I might give birth earlier (even though I carried to 40 weeks with my first)