I recently had sex & my labia is now very swollen & more red than usual. i'm wondering what could have caused this?

Many things: Among the most likely things are increased blood flow to the area - which is normal during intercourse, irritation, or potentially an allergic reaction to the condom or lubrication.

Need exam: You need to be examined by a healthcare provider and screened for STDs. It's hard to answer correctly without proper exam and/or testing. See your PCP or Gyn.