is a low risk for most STD's out there. The biggest one mostly seen is HSV due to skin-to-skin contact. Ejaculatation doesn't matter when it comes to STD's for the most part because guys do have pre-cum that can be found when we get oral sex
is just not the best way for STD's to be transmitted. I believe gonorrhea and nongonococcal urethritis are the two that could also have been transmitted but not really going to happen because its not likely to be in the mouth.
If you have symptoms be seen within 24-48hrs by your doctor.