Unable to load Marketplace and Skins

I have been unable to load my marketplace or use skins for the past 2 days now; any time I try to press the Marketplace option, It says 'Invalid Session'. I have tried resetting the game multiple times in a row, and nothing has changed! Please help!

It is starting to worry me that something is either wrong with my game, or my version. I do not want to uninstall Minecraft because I do not want to lose any of my worlds, but I also would really like to use my own skins.

Thank you, hopefully it is fixed soon.