yellow line on the left hand side of my screen iphone 4 after 18 months why has this occured whats the soloution?

I have had my iphone 4 for 18 months on contract..I have had no problems at all up until the begining of this month. The first issue was that the home button, double click issue wasn't working too well. I read that their was a way to calibrate the button which I had done ( please note this does not include opening up the phone) and I noticed that it works much better. However lately I have noticed that I have a yellow tint, line vertical on the left hand side of the screen. It is very faint when I wake my phone but then gets darker and darker.

I have read that people have noticed this on buying their new iphones however mines has just appeared. my contract is up in 6 months so I'm not keen on spending extra on the phone is there anything else I can do?