I keep mine refrigerated and mix it up before I use it. Seems that tsirring it well helps. Also, what type of bread are you using? If it's just the crap off the shelves, it's too soft. The PB won't stick to it very well. We use Food For Life brand Ezekiel 4:9 bread. It's whole grains and a 'heavy' bread. Also contains no artificial flavors, preservatives, colors, or anything else weird. Totally natural. It's in the frozen section at health food stores and in some regular grocery stores. It's really good for making the PB spread easier.
My 3 yr old asks for spoonfuls of the natural PB.