What Causes Lower Back Pain And Nausea During Mensuration?

Hi, I had a natural miscarriage 6 weeks ago and have just started to get my peiod today. Is it normal to have extremely sore lower back, every movement hurts and to be feeling nauseous. Normally I only have slight lower back pain. My breasts are also sore, is it just them going back to normal. I was only 5 and half weeks pregnant. Thanks