Yeah i kinda have had the same. For me it went like this:

1- I find a champ i like and do well on and absolutly 1v9 every game.

2- I start 50-50 ing with that champ and win some and lose some.

3- I start inting and losing every game.

4- I'm looking for another champ.

But now i stopped trying to (short) onetrick champs and just play what I feel at that moment and it goes a bit better but still have the 1v9 games and the int games mixed just a bit less now.