Five days ago, on Monday, my iPhone 4S stopped being able to connect to any Wi-Fi stations. It couldn't connect for two or three days and then one day suddenly connected again. All my other devices, like my MacBook Pro, Kindle Fire HD etc. Could all connect, apart from my phone. It was able to connect for one day and then just stopped connecting again. I tried three or four Wi-Fi stations but it always came up as "Unable to join the network". I've tried restarting it, resetting the Wi-Fi settings, forgetting the network and manually selecting it, but nothing works. What should I do to get my phone to work again?
(I don't want to go to an Apple Store, unless I MUST go, it can only be a last resort)