Sudden Duplicate Photos

So I went onto my photos tab on my iPhone 6s this morning, and it has suddenly duplicated all of the photos on my camera roll, even though they were singles when I took/saved/screenshotted them. My iPhone already says it has low storage space, so why would it suddenly take up even more by duplicating everything? I haven't recently updated to a new iOS either, so I doubt it would be related to that. If anyone can help explain this or how I can easily get rid of, or at least hide, the duplicates from my camera roll, that would be much appreciated 🙂 thanks!