IPhone Wi-Fi only works when it's really close to my home's router...

Hi, I need some help here please!!!

I got an iPhone and my brother too, he's got no problems when connecting to the Internet through Wi-Fi at home, and so didn't I, until some days ago when suddenly it seems like it stopped working, it says that it can't join the network whenever I select ours from the list of Wi-Fi networks, but then I noticed that if I place the iPhone really close to the router (on top of it) it works perfectly fine and it opens any web site and displays any you tube video, checks email, etc...

Can you anyone please suggest anything I can do to fix this... i have tried resetting the network settings, forgetting the network and renewing lease, but the problem is that it does not work whenever the iPhone is not extremely close to the router, it doesn't even work if it's in the same room, it has to be on top of the router in order to work fine.

The router is not the problematic because my laptop works fine and even my brother's iPhone.

Please help me out!