I'm in a similar situation, here's part of a post I made a while ago about my situation.
According to op.gg I currently have a 54% winrate, going by that alone I should be climbing and ranking up, even if slowly.
Almost every game I win I gain 17 LP, and almost every game I lose I lose 21 LP. I know because I see those numbers over and over again after every game.
Knowing this I decided to do some math. Lets say I have a 55% winrate over 100 games.
55 wins times 17 LP = + 935
45 loss times 21 LP = - 945
Even with a 55% winrate I would still lose more LP than I gained.
Lets say I have a 60% winrate over 100 games.
60 wins times 17 LP = + 1020
40 loss times 21 LP = - 840
Right now if I managed to get a 60% winrate I would only gain 180 LP over the course of 100 games.
Lets see what would happen if the amount of LP gained and lost per game was both 20 with my current winrate.
54 wins times 20 LP = + 1080
46 loss times 20 LP = - 920
If the amount of LP gained and lost was the same I would gain 160 LP over the course of 100 games.
That's almost as much as if I had a 60% winrate right now.
This post has some relevant math in regard to LP wins and losses
http://boards.na.leagueoflegends.com/en/c/gameplay-balance/Fy2Krrx0-lp-gained-and-lost-makes-it-impossible-to-climb