You said 56% winrate. I did not look you up, I took your word for it.
The only way dynamic queue would lower your MMR, is if you are silver and queue up with Bronze 5 and loose a lot.
With bad MMR, you need to keep on winning more than you lose, and slowly it will increase. You need to forget about LP, and keep on winning more than you lose. The LP is worthless, and so is your division. Your ELO needs to go op.
I am Platinum V atm. But not too long ago, I was trying to get here and was Gold 2 80LP. I went, with a massive loosing spree down to Gold V 0 lp. I went from gaining 25 lp from games and losing 15, to losing 25 and winning 17. My winrate went from 54 to 49. And yet now i am Platinum V, from winning more than I lose, and eventually my MMR went up, once it did I could easily climb again.
When pros do unranked to masters, they gain regular amounts of LP. at the beginning. But once they have 50 wins, 10 losses, believe me, they start gaining a ton.
Want better MMR? Win more than you lose. If in champion select you ever think "Wow this team sucks, we are so going to lose?" Dodge, lp goes down compared to your MMR, and if it happens a lot, your gains go up. The more you dodge, the more your gains go up, plus you cut losses.