Iphone 4s Wifi Problem

Hi, I've had my Iphone 4s for a fair few months now, and never had a problem with it's connection, but recently we've got a new router, and that was fine. Then I got the newest ios 6 and my wi-fi on my phone then worked for about three days, but after that it completely vanished, and now it won't even be allowed to be found on the wi-fi settings, how do I fix this? because using 3G all the time, racks up my bill.

So I don't know whether it was the new router or the new ios that wrecked my connection, I might be wrong and it could be something completely different. Help? :confused: