Only 6+5 and feel ready to burst already!

Laura
Hey ladies, 
As I've said in the title, I'm only 6+5 with DC/DA twins and although this is my fourth pregnacy I have no experience with multiples.
Surely this sort of rapid growth shouldn't be possible?! In the last week alone I seem to have doubled in size and I have another 30+ weeks to go!! My belly and hips ache and its soooo itchy plus I have awful shooting pains in my lower stomach and groin! 
Please tell me it's normal.... And it gets easier?!?!
Thanks guys!!