I feel you. I was the same way with Katarina last season. I logged in over 650 ranked games with her, carried myself from bronze to high plat in only a few weeks, but now, I cant even carry with her in gold elo lmao. So what I did was playing some norms and teambuilder to find a champion I could once again get excited about. And I have found that that champion is Zyra. So my suggestion to you is, try playing champions who's kit's you think are interesting and go from there. Also, don't be afraid to try a champion that you didn't want to before. I told my self in season 3 that I was never going to play kat, but then I played her at the beginning of s4 and it worked wonders for me. Expand your horizons :D