MB2 being replaced w/ A+click HALP!

So, one day i was playing like 2 games of lol when i noticed that i could not stop attacking. I could not buy items, or do anything other than attack when an enemy was near. Help pls. How do i fix? I reset it by quitin' LOL and reconnecting, but it has cost me a game already. I play on mac btw..

ty