I have balanities I have got cream for it but my girlfriend is getting a stinging pain in the vagina after sex will this be causing it?

Yeast infection? Balanitis is often yeast (thrush), especially in uncircumcised men. Vaginal yeast is common and a frequent cause of vaginal itching, irritation, etc. So it seems likely you and your partner are sharing a yeast infection, not uncommon in sex partners, although not considered an STD. She should see her doc; or maybe try an OTC vaginal yeast treatment. But for sure get care if no better 3-4 days.