I am no expert, I just have a reasonably sane head on my shoulders and the ability to question.
I hate talking about pregnancy, but the number of silly rules is making me say, Nic, pay no attention! It is possible for a woman to go through all 10 months (yes) without knowing she is expecting, and therefore not heeding any "advice".
Check it out for yourself, but you will find:
You can eat pretty much anything you would normally eat ( seafood, sushi, eggs, peanuts...). Unless you're a die-hard tuna fan or cheese rind addict you really should be fine!
You can sleep any way you can, even on your (gasp) back.
You can drink alcohol.
You can drink tea and coffee.
You can exercise.
You can dye your hair.
You can travel in a plane.
You can't do anything to avoid stretchmarks, you either get them or you don't.
There is only a 5% chance your baby will be born on the due date. Not really a myth, but ignore the due date. French pregnancies are 42 weeks. It'll come out when it's ready.
The one myth I think could be disputed as true is the whole "eating for two" thing. Heck, you've got to have SOME fun!! Go get some cake and chill the hell out.