Battery life less than 12 hours; Wifi says "UNABLE TO CONNECT"

I just got my iphone 3 weeks ago and it work perfectly. It usually drain at arounf 2-3 days depending on the usage until one night i left it with 69 percent battery so i supposed i should not charge it yet because battery level is not that low and surprised when i woke i my battery was drained already so i rushed to my computer and charge it for a couple of hours then bacame full charge. Surprised again my battery life gone so short time like less than 12 hours. Please help with my problem. Also my wifi used to work i usually surf in the net using my iphone but now it wont work, it can see active connection but it says "UNABLE TO CONNECT TO BELKIN450(router name)". Plese i need you help. Thanks