What is wrong with the Wi-Fi and my iPhone?

My iPhone used to get Wi-Fi in my room. Now I only get Wi-Fi in the rooms next to the Wi-Fi and in the room with the Wi-Fi router. Now when I'm in my room the Wi-Fi symbol shows up in the top left corner and it shows 1-2 bars. But when I try to use the Internet it doesn't work and eventually switches to 3G. So what is wrong and what can I do.
The Wi-Fi works with the ipad and all other devices when in my room

Sometimes a case or other device can affect connectivity. Have you done any changes to your room or iphone? Some devices can interfere with Wi-Fi, even microwaves. I believe the iPad works because it has a longer range.