Leaky diaper

I have been struggling with a leaky diaper every night for the last two weeks. I have gone down a size, gone up a size, changed brands, changed styles, watched videos on how to "properly put on a diaper" and obsessed about everything being covered. All of this to no avail. Then I happen to read, on the many diapering sites I have visited, that petroleum jelly can rub off on your diaper and cause it to loose absorbency! Has any one noticed this? Did I just spend hundreds of dollars on bags of diapers and all I had to do was stop using petroleum jelly?