Why The Vagina Lips Are Swollen And Painful After Having Intercourse?

Hello.I've just gave birth to my second child 8weeks ago.both me and my patner go for regular check ups for sti's and are clean.I have had sexual intercourse with a condom.straight afterwards my vagina lips have swollen.its bin painful to have intercourse since I gave birth but this is the first time this has occured.what to do?