White spots on my Dell XPS 13 screen

I've started to realise more and more white spots, areas which are brighter than other areas on my lcd screen. I know for sure it is not  a problem with the graphics as I have taken screen shots, connected the laptop to an external monitor and so on. The white spots do not appear on external monitors and screen shots. Thus it is a problem with the lcd screen, what should I do? My warranty runs out in 2.5 months.