I'm sure its nothing to worry about. I remember having this late on in pregnancy and its just the baby pushing down getting ready for the head to be engaged. Doesn't usually mean you will give birth soon! I used to get aches and pains going in the areas you describe and down my legs too.
I am 10 weeks pregnant with my 2nd and sometimes get a funny ache down below now so who knows what I'll be like by the time I have a huge bump!