Laura, My 11 yr old daughter went through the same things about the same age.  I would swear she had an infection due to burning, smell, etc and we’d test her and no infection.  What was happening was that the urine was pooling in the vaginal canal and before leaking out she would have symptoms of an UTI.  My past posts may be more specific (check the archives).  You can email me if you want, Natalie