Some STIs have no symptoms at all. Others appear and then disappear, while the infection remains. So you cannot always rely on symptoms to show that you have become infected. Some common symptoms to be aware of are: pain or burning while urinating, rashes, sores, blisters, itchiness, unusual discharge from the penis or vagina and pain during sex. If you think you might be infected with an STI, see a doctor or healthcare provider ASAP. Delaying treatment can cause the infection to get worse!