What is the cause of a sudden overactive bladder (had it since 2007) and how can I cure it? How exactly does a doctor diagnose this condition?

See a urologist. Oab is diagnosed by history, urinalysis, and urodynamic testing done by a urologist. There are several treatments for this condition to include oral meds, behavioral therapy, nerve stimulators, and recently Botox bladder injections have been approved for use in oab. There however is no real cure.