baiza,
I've had both those issues and it is currently because the baby is posterior meaning it's back is facing my back, therefore back to front. Results in back pain. The pain in my lower pelvis is due to everything stretching and getting ready (gosh I was it was ready now!!!) and I've been having those pains for over a month or more now. If you're super worried ask your doc or midwives why etc... no need to worry just call them!