i am really lucky as I don't suffer from constipation - i put this down to the fact i drink a lot of water and eat lots of fresh green vege everyday, with a fresh juice (celery, apple, cucumber and mint - yum) and take my pg vitamins (elevit). however I totally hear you on the back pain and leg cramps; DH gives me a leg rub almost daily which helps immensely and i use my heatpack on my back a lot this time round.
lots of luck