Normal PvP Matchmaking Selection

After a streak of losing 10 or so games by slight margins with , the game following I won 18/6/12 with her. I VERY much doubt I suddenly got better like that, or if I started sucking for a long time for some reason. Does Normal PvP (Not ranked, I'm a noob) have some sort of selection process/criteria, or is it completely random? Were the games I lost in a row simply my fault for being bad, and I finally got it in the last game or what? I want to figure out if there's a system I don't see, or if I should figure out what else caused it.

Thank you.