I'm a fan of tissue salts! They work on a homeopathic principle which involves extremely low doses (but big effects!) which is usually safe in pregnancy.
But before you take my word for it, call the company. When I worked as a vitamin consultant in a pharmacy, I used to call natural health companies all the time to ask if their product was safe for pregnant women. A lot aren't, but I can't remember what e.g. Martin & Pleasance said...
GL!