My iPhone 4S wifi only works if I'm in the same room as my Router...

Hello everyone. Last week I posted a question about not being able to connect to my wifi on my 4S. Now actually i can but it only works in the same room as where my 'router' is. In my bedroom even if i have 3 wifi bars the pages dont upload or youtube etc doesnt work either. I mentioned this to my cousin and he said it might be my phone's wifi antenna thats gone bad. So now before i go ahead & change the antenna I'd like to know if there could be something wrong with my wifi router or is it indeed my phone's wifi antenna. Please note my wife's iphone 5 works as normal in the same spots around the house as mine doesn't.

Just help those out who have the 'greyed out' wifi icon, mine actually came back after i charged my phone with the Airplane mode on. My wife'd said if you charge with the Airplane mode on it charges in half the time. Dont know if thats true but it got my wifi to enable.

Thanks all.