The oral sex was less than 24 hours ago, or you've had the irritation for less than 24 hours?
If the oral sex was less than 24 hours ago, I'd say it's irritation. That's too soon for any kind of infection to show symptoms. It could be an infection from something unrelated to the oral sex, though.
In any case, a hickey is the result of biting or sucking on skin and forming a bruise, so it's not that. If it lingers longer than a day or two, you should get it checked out. Be honest with your doctor that you performed oral on a man, with the timeline of events, so they can properly assess you.
In the meantime, try rinsing with warm water and salt, or try one of those sore throat sprays. I wouldn't try anything with an antibiotic in it, as that could mess up testing later.