Why is my iPhone 5 running out of storage

My phone is constantly telling me my storage is full and I can't save certain things because it's too full. I have 400 pictures and I don't have a ton if apps. I have a white 16 GB iPhone 5. It's updated to iOS7. I had more space on my phone when I had 4,000 pictures. I can't figure out what is wrong. Do I have to buy the new storage plan? Or is there something else I can do? I need answers As soon as possible please!

IOS updates take up ALOT of storage that's the problem.

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