Iphone 4s Wi-Fi problem

SO basically, over the last few weeks, the wifi on my iphone has been dropping out and switching to 3G, which I don't want. When I click on the Wi-Fi section in the settings, it takes a while for it to actually get on to the page and just searches for networks forever, not finding any. Just today, the wifi 'greyed out' for the first time. I searched a bunch of methods to fix this and one of them was to overheat the actual phone, turn it off, let it cool, turn it on and it should be fine. It worked, and then 15 minutes later, boom, back to 3G. This really frustrates me and I don't really think its the wifi module within the phone. Also, there is definitely nothing wrong with my modem/router, it works fine on my other apple devices.

First off, i'm going to cover the things you're probably going to ask:

How long have you had it: I have owned my iphone 4s for about a year and a half now.

Have you reset your network settings: Yes.

Have you tried resetting your phone: Yes

Hard reset: Yes

Have you updated to the latest software: Yes

Have you tried areoplane mode: Yes

Current software: iOS 7.1 (Up to date, and I have had iOS 7 for a long amount of time now, so its not iOS 7 because I've never had a problem with it)

Do you want to visit the apple store and ask the 'geniuses' for useless help: NO.

Please guys I would really apreciate some help here, and please don't waste time and answers saying that I should go to an apple store, that is useless help.

Thanks!