Books not downloading after purchase

My book shows up in my list of purchased books with the little square with the blue circle around it saying it's downloading but it's not moving and it never downloads and I cannot open my book. This has happened several times, does anybody know what to do. This all started since the new software update when the iPhone 6's came out. I'm about to give up on iBooks and just purchase on kindle app. This is ridiculous that I have to fight with it to read a book.