Swelling is normal, increased blood flow and pressure changes make it very common. As for the pain, unfortunately that is common too. I have experienced it with all 3 of my pregnancies. Many women I know have as well. Once baby drops and everything starts to loosen and stretch to prepare for labor, there is nothing for support. When baby moves or you sit in certain positions it increases pressure. Also sneezing correct coughing can make it feel worse
I agree with the above, I'm 32 weeks now and have had the same for about 2 weeks. My doctor also told me that along with the round ligaments loosening, the ligaments in the pelvis (I think that's what she was saying) are also loosening and can cause that irritation.
Vaginal irritation does happen in pregnancy. There's an increased blood flow there which makes it easily irritated. Just let your Dr know so they can check or yeast or vaginal infections those are more common during pregnancy as well.