swollen vagina?

Okay, not really my whole vagina, but a part of it that i didn’t even know existed and i can’t find it on any pictures? anyway, i’m 21 weeks pregnant and me and my boyfriend had sex a few days ago and his penis swelled up a good amount but there was no pain, and that’s when i noticed this part of me was swollen. it’s been swollen since then, but no pain. we had sex again today and his penis swelled up again and now there is a ton of pressure on my vagina and it is uncomfy to sit up. this is my first time being pregnant, i don’t know if it could be because of the pregnancy, but if anyone knows anything please comment, i am so nervous.