Ahhh first time mum, I totally understand the worry! But honestly, you should check with your doctor about those cramps and back pain, they can give you the clearest answer and make sure everything's okay. A few of us went through similar things during pregnancy, and it turned out to be normal stretching and ligament stuff, tapi better safe than sorry lah, especially since it's affecting you quite a bit. Just get it checked out so you can relax, ok? Take care of yourself!