With unprotected oral sex, there is a risk of transmission of STDs, particularly for infections like gonorrhoea and herpes simplex virus (HSV). The throat can harbour the bacteria that causes gonorrhoea and this can spread through unprotected oral sex.
For HSV infection, the risk of spread is highest if the person has a history of cold sores and has active blisters or ulcers. The risk of spread is significantly less in the absence of active lesions.
Viral warts or HPV infection can spread through oral sex too.
For HIV infection, the risk of contracting it through oral sex is lower than vaginal or anal sex, but there is still a small risk. In the absence of cuts and bleeding in the mouth, the risk is low. It is therefore always important to engage in safe sex and use a condom at all times.
If you are concerned, you can consider going to see your doctor for STD screening. Your doctor can assess your risk and advice you on the necessary screening tests.