iPhone 5 Slowdown

My 6-month-old iPhone 5 doesn't feel as snappy and responsive as before... Especially when I double-click the home button, there is a slight delay before the multitasking tray comes up. I've deleted all the conversations in Messages and all Safari data. I even tried quitting all apps, although I knew that technically that wouldn't help much.

I believed that consistency in performance is a strength of Apple products.... What could I possibly done wrong? Is it because I've installed and deleted too many apps? Let me know also if your iPhone 5 feels slower than before.

P.S. I am fully aware that it's natural for any smartphone to slow down over time, but I feel that 6 months is just way too earlier than my expectations.