My mmr or elo or whatever the heck it is.

Okay so I am a gold 4 player and I have 1679 mmr according to na.op.gg. Except the average mmr for my games that na.op.gg is giving me is around 1500. Why is this? Also, I just won a game and got 25 LP except my mmr dropped... This was not a duo queue game that I was playing with a bronze friend or anything like that. This was your normal solo queue. Why am I losing mmr when my solo queue match making should be against my mmr level anyway?