My home Wi-Fi on my iPhone 4 keeps disconnecting?

So, me and my father both just bought an iPhone 4, and for some reason, my phone disconnects from our router everytime i go like 20 feet away from it, while my dad's iphone is still connected. I had both of the phones side by side, and in the Wi-Fi settings, it showed all the available Wi-Fi's nearby on my dad's phone, but it showed nothing on mine. My phone is updated to the latest ios, and all of my family's smartphones are connected to the Wi-Fi except for me. Just my luck, right? I tried many of the solutions on the internet like restarting my phone, turning off Wi-Fi and turning it back on, and many others. Can anybody solve this little dilemma that i'm in, or should i just go to the att&t store and get a new one?

Added (1). There's only 4 people (including me) in my family who uses Wi-Fi. Would that possibly be the reason why?

You likely have too many devices on your router. There's usually a four device limit. Once the limit is reached, it is no longer available.

iOS has been notoriously buggy concerning Wi-Fi since 5.x. Apple does know about the problem, and it was supposed to be fixed with 6, but that hasn't happened. This problem mainly shows up on iPhone 4, 4s and iPod Touch 4

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