If the bump is in the area where the "ear" would be (if turtles had external ears)it is probably a middle ear infection. I would suggest a herp-friendly vet, if you are not accustomed to treating medical conditions yourself. Usually, the swollen area is sterilized with antiseptic, such as Betadine solution, lanced, drained and flushed with more anitseptic. If the pus has congealed, it must be dug out with a sterile probe. Prior to lancing, however, the turtle should be put on a course of injectable antibiotics that is continued afterwards. Two options are Baytril (enrofloxacin) at 10mg/kg of body weight per day for about ten days, or amikacin at 10 mg/kg of body weight every other day (or, my course of two days on, one day off) for a total of six doses. You must have an accurate weight and very carefully calculate the dosage and injection volume of antibiotics, however. Somewhere in the forum archives a year or two back, someone presented a nice photo series of his meticulous treatment of this condition. It would be worth while trying to find it.