Same thing happened to me, and it was only that once as well so I think it's nothing serious.
it only happend that one time after i had sex. then it stopped.
You could have a UTI. Sometimes intercourse causes that. Super awesome right?
Drink a few glasses/bottles of water and pee a couple of times and see if it still burns. You body could have just been flushing out bacteria. As long as it doesn't continue you're probably fine.