Is the pain in your upper jaw, if yes then is it at the back end of your jaw..?
This might also be a case of Wisdom Tooth eruption or decay of wisdom tooth due to food lodgement in that area as it becomes difficult to clean using a toothbrush due to its deep position usually covered by a flap of gingiva.
Next Steps
Don’t delay, immediately visit nearest dentist.
Health Tips
On an immediate basis, something non invasive, like chlorhexidine mouth wash rinsing could be helpful dealing with bad breath.