What Causes Severe Fetal Movement,lower Back Pain And Cramps During Pregnancy?

I am thirty six weeks and six days pregnant. I am having extreme baby movement and I am in pain. I lost part of my mucus plug about an hour and a half ago, but only a little bit. I am trying not to freak out, but every time she moves, it feels like everything is about to fall out. My back is on fire and I ve had cramps for three days, but nothing has felt like this. I think its her moving, but I am not sure. I am a first time mom with no one to talk to whose been through this, can you help?