Why can't I redownload an app?

I deleted my snapchat app because it keeps lagging out, so I thought if I delete it again, since I've done this before, it would go back to normal once I redownload it again. But once I got to the app store and try to redownload snapchat, the cloud turns into that circle loading thing, and suddenly quickly went back to the redownloading cloud. I tried redownloading it a couple times, and shutting off my iphone to try again, but it wouldn't download at all! Please help me. My iphone is 4s, ver. iOS 8.3.