Finding Myself Not Doing So Well In General

Last several games have been horrid. Losing as Diana in all four games I played as her yesterday, then lost as Teemo top vs a Malphite and Lissandra mid vs a Zed. And those last two weren't even ranked. Anything faulty with me and my gameplay/demeanor?

(And no, just telling me that I lost because I"played X in role Y against a Z" isn't what I'm looking for in advice. I want to play who I want within reason, and seeing that the reason I failed is in playing said champion in that situation is not good for motivational reboosting).

EDIT: When I see myself losing games in a row, that's an indicator that there was something I did wrong, either in getting my opponent fed (which I try not to do), playing too passive in an effort to avoid death, or doing something stupid and desperate like diving low health enemy champions and getting wrecked in an attempt to save the match. I feel like I don't know how to properly solo in a game in which the enemy champions get to a point in which they become too thick/strong/grouped up to kill, or revolve too fast to outmaneuver/split. I think it was said of me in something previous that I only know how to do well in games where everyone else is doing well in the first place, but have difficulty coming back from being behind. I don't want to feed or be the reason that the game is lost, so I'm not too keen on risky early-game moves, but neither do I like games where I get shut down or put out. Currently trying to find champions other than Heimerdinger to do well on - someone who has an answer for every situation within reason (aka I'm aware that there is no champion that will always win the game). So am I the reason I lost, or have I had very bad luck with the other players I queue with, or is it tilt screwing with my mindset? Refer to LoLKing, op.gg, Match History, etc. for specific points of data.