STDs don't always cause symptoms or may only cause mild symptoms. So it is possible to have an infection and not know it. And even without symptoms, STDs can still be harmful and may be passed on during sex. If there are symptoms, they could include: Unusual discharge from the penis or vagina Sores or warts on the genital area Painful or frequent urination (peeing) Itching and redness in the genital area Blisters or sores in or around the mouth Abnormal vaginal odor Anal itching, soreness, or bleeding Abdominal painn Fever