Despite the information that circulates on the Internet, oral sex is actually generally pretty safe, and oral sex is usually an inefficient route for transmission. Unless your partner was displaying any symptoms (discharge, sores, lesions), you probably have no risk for herpes, syphilis, or hpv. The STI that you would most be at risk at is gonorrhea, which can lodge in the throat. Most cases go away on their own, but you can have an oral swab done if you have a continual sore throat.
There is risk of getting oral gibrrhea, syphilis, herpes or hpv as well as other infections from this encounter. I would suggest limiting unprotected oral sex to partners that you know well.