You might have seen or felt something weird down there, but it does not necessarily mean that it is something serious. Since I would not like to turn you down, let me give you information on those sexually transmitted infections that do not always mean something terrible, even though they are common.
Probably yeast infection is on the top of the list, since this is what can simply occur without even a sexual intercourse, either as an aftermath of an antibiotic treatment, or simply of a weak immune system or stress. Its symptoms are itchiness, redness, curd-like vaginal flow or tiny spots on the skin, but men may not even notice they have it. Still, both partners need to be treated with systemic and local anti-fungal medications.
Since it occurs due to an imbalance of the bacterial flora, it is quite frequent that it is accompanied by bacterial infection, as well, but it still does not mean that your partner have had sex with someone else. Smoking, or frequent douching can also lead to BV, and it can also be transmitted sexually. Its symptoms are gray, yellow or white vaginal discharge that smells like fish, especially after sex. Treatment is antibiotics for both partners.
Unfortunately, though, there is quite a common virus, especially among Americans, which spreads via sexual contact and it cannot be cured for all. Its symptoms are itchy and painful blisters, which can occur either near the lips or on/in the sexual organs. Herpes can be treated orally and locally, as well, but it will stay inside the body, and any time the immune system is weak, the patient will experience an outburst.
These are mild conditions, but there are more severe ones. If you have fun with one of the webcam sex models, however, there is no risk at all.