15 weeks and worried

I am 15 weeks today. I have had cramping pretty much all day. It's not like the stretching that's on and off. It's been all day cramping and now I'm having a burning lower back pain. Is this normal and I just didn't experience it with my first? It's a constant pain and it's making me uncomfortable. Not unbearable. Just uncomfortable. It feels like I have my period. I don't want to call my doctor after hours and sound crazy.