Hallow Dear, Since you had intercourse with the use of condom, there is less likelihood (though not impossible) that you have contacted sexually transmitted infection. You have taken Postinor 2 next morning. So there is almost no possibility of pregnancy. Now the question of yellow vaginal discharge remains. Such a discharge is most likely to be due to some infection, mostly bacterial infection. If either during sex or during masturbation you have not observed proper hygiene, such infection may take place. Yellowish discharge is caused by bacterial infection for which you may need antibiotics treatment. Please report to your Gynaecologist or STI specialist ASAP for appropriate diagnosis and treatment. Ignoring the symptom may lead to serious complications like chronic pelvis infections and/or tubal block leading to infertility. I hope you got the required advice and message. Dr. Nishikant Shrotri