Why did my lp gain change?

I've climbed from B4 to S4 this year and basically i've been having good scores, having good mmr (my mmr is Silver 2) And every game i get 17-19 lp and every time i lose i lose 20-22 lp. Why? Its just hard to climb if this happens to me and it basically demotivates me because its basically telling me that i get less than what i work for...Any ideas why fellas?