Bladder infection! (TMI)

What causes bladder infections? 
I have bad itching down there and hurts,feels like my pee hole is ripping open! And my panties are constantly wet so I have to wear a pad even tho there is no blood. 
 My doctor said on Tuesday that its probably a bladder infection but the test results won't be back till Monday or Tuesday due to the holiday. She gave me antibiotics for it and I went and got some AZO but nothing has helped!! :(