LP

Hey, I got promoted to S4 and played my first game in it and won, and it said +22 lp, but it only gave me 19. I find this really strange as its never happened to me before and I can't think of how to explain it. My mmr is average I would say, I got anywhere from 21-24 lp per win, and lose 12-14 per loss. I just don't know what to make of this and I exited the screen before I could take a screenshot but I'm not lying, otherwise I wouldn't be posting about it looking for an explanation. So anyone care to try to explain?