You would've probably had a palatal injection about there. The injection doesn't normally cause anything except a bit of bruising. If your teeth were abscessed, then perhaps it's part of the abscess surfacing? Really hard to be sure. I'd give it a couple of days. Mother Nature often cures things if given some time. And you seem to have a lot of erosion of your teeth - do you have lots of acidic drinks or juices? (soft drinks, fruit juices).