Lux e wasn't working

After I reached lvl 7 in game, i went bot lane to try and fight vayne and thresh. I was on red side and came through the tri bush. I then threw my e over the wall into the fog of war, and then for the rest of the game I was unable to use my e. It just went gray and said "this ability is unavailable". I even tried it after upgrading it, but still no response. It caused me to lose a winning lane and rendered me unable to supp my team. Pls Fix! Also I'm sorry ahead of time that i couldn't get any screenshots, I tried several ways but none of them worked. Sorry.