Loading takes a very long time

I launched minecraft and it was loading as usual, so i left it on the loading screen for 5 minutes then i come back and see the loading bar had not moved at all, i come back 5 minutes again and the loading bar still hasn't moved, i come back 20 minutes later and the loading bar is halfway full, im not sure if loading should take this long, this is pretty annoying as it happens whenever i try to launch the game.