Hi!
Congratulations!
Probably the very best dietary recommendations are put out by the American Diabetes Association.(diabetes.org) They make recommendations for women with diabetes and gestational diabetes, but even for women without those conditions, their diet is great. The American College of Gynecology (ACOG.org) site probably has some good information too. The only difference is that you can afford to indulge an occasional craving or two.
If your diet is not optimal, a prenatal vitamin is really a good idea--if you can tolerate it.
Make sure to get plenty of calcium and iron too. You also need vitamins C and D to absorb those minerals.
Good luck!
Dr B