Receiving oral sex (i.e. having your partner suck your penis or lick/kiss your vagina/clitoris), carries NO risk of HIV transmission. Performing oral sex (i.e. licking/kissing a vagina/clitoris or giving a blow job/sucking a penis) is extremely low risk in terms of HIV transmission. There are a few case reports and individual experiences that support getting HIV from performing oral sex on a penis, but it’s extremely rare. As far as whether oral sex is riskier if you swallow semen, truthfully no one really knows. Having bleeding gums, recent dental work or large sores in your mouth may slightly increase the risk.
Other STIs like syphilis, gonorrhea, chlamydia, herpes, and HPV are transmitted through oral sex. Many of these infections are easily diagnosed with simple tests and can be treated with available medications. If you are worried about your risk for HIV or STIs, talk to your health care provider about getting tested and ask them if PrEP (pre-exposure prophylaxis) makes sense for you.