While oral sex and blowjobs are much safer than both vaginal and anal sex and the fact that most STDs are either unable or have trouble transmitting through oral sex, it’s still possible to contract an STD (sexually transmitted disease) , STI (sexually transmitted infection) or VD (veneral disease).
While both chlamydia and HIV can be transmitted through oral sex, the risk of them doing so are very low compared to vaginal sex.
The diseases that you “need” to worry about are genital herpes, gonorrhea and genital warts.
They’ve shown that swallowing semen slightly elevates the risk of contracting an STD, but it’s not something you need to worry about. Swallowing semen is however completely safe if your man is healthy.
If you have a single steady partner then you probably don’t need to worry about this; but just to be on the safe side, I suggest you both go and get checked out before doing anything.