Afterbirth pains or something more?

I gave birth to my second son 6 days ago and have been having afterbirth pains occasionally but tonight they were almost excruciating staring on the left almost at my hip joint and radiating across and through my tailbone and even down to my rectum. I had a natural uncomplicated birth with no stitches or tearing - does this sound normal?? They have reduced since taking painkillers but I am still achy like a slight menstrual cramp