Maternity underwear is made extra-stretchy and either low-cut, to fit underneath a growing bump, or high-cut, to fit over it.
Your lacy undies in your lingerie wardrobe can only fit up to first trimester, before your bump is obvious. From second and third trimester, try low-cut undies, that would go under your belly, or high-cut panties that go over beyond your bump. It's true that high-cut panties aren't the most flattering, however it's the best choice for many as they're most comfortable. Try to pick soft, stretchy fabrics that won't irritate your sensitive skin.
You can wear normal undies during pregnancy. During pregnancy, vaginal discharge may increase. Pregnant women are also more prone to yeast infection. Cotton underwear is best to prevent infection.