What causes an overactive bladder and fever?

Infection. Overactive bladders are usually related to irritation of the bladder or nerve dysfunction. When the overactive bladder is associated with a fever and this is a new problem for you, this is probably an infection. You can self treat by drinking a lot of water and trying to acidify your urine with high acidity foods like citrus fruits and tomatoes. However, if you are fevering, call your md for abx.