My iPhone won't connect to wi-fi?

I have the iPhone 3gs and it's using version 4.3.3. I've been using wi-fi at home since I got it (6 days ago) but for some reason today it won't connect to the internet. I restarted the iPhone, turned wi-fi on and off, I did the "forget this network" method, I restarted the network setting, and I tapped on the "Renew Lease" button. All other devices, my macs and pcs, can connect to the internet except for my iPhone. My phone has the wi-fi logo at the top and claims it's connected but when I open safari or something, it says there's no connection. Also, it would sometimes get connected again on its own but then disconnect a few minutes later. How do I fix this so that its TRULY connected and stays that way?