It could either some Infection which came in bcz of ur partner,or it is some harmonal changes,and it may also be in relation to if it was your first time ,and lastly may be your Menstrual cycle is about to begin.
Next Steps
I suggest u wait for another time ,and if again it happens in your next contact u can get an examination done.
Health Tips
suggest also that you maintain your personal hygeine,change your undergarments atleast twice a day,and stay hydrated by drinking lots of water