If you're worried you have got an STI, go for a check-up at a sexual health clinic as soon as you can.
Don't have sex, including oral sex, without a condom until you have had a check-up.
You can have an STI without knowing it and infect your partner during sex.
Many STIs have no symptoms at all, like HIV. The only way to know for sure is to get tested.
Find a sexual health clinic