You might have some compression of a nerve root
in your back since the only time you state you get this pain is at night.You have covered the obvious sources such as cardiac and gi. Your pregnant so you should not get x-rays unless in an emergency. You could see a chiroprator for an assessment only or physiotherapist. Your famiy Dr could send you for nerve conduction studies or to a neurologist
. I've hurt my back and I've gone through the same thing, it's not pleasant.Does the pain stay constant or does it ease off?