ABOUT RANKED (please do something)

I would like to make a question...why when i'm "climbing" ranks when i go in a rank like bronze 3 (from bronze 5) i'm starting falling??? In most of the times i'm playing really good but it doesn't let me rank up...I don't think that this is fair riot...Could you please search about that? It is like my MMR is resetting...i'm doing like 6 wins in a row i rank up and them i lose 10 game in a row or something...please try to do something, i can't stand up with this for more time...