Your opponents rating is too low for your rating to change thats why
Online Chess Rating Not Changing
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The game with Gomezgu ? It was unrated: Unrated 
Oh was it? That explains why. Now I feel stupid
Ok, so I don't know if there is an actual reason for this, but I just won an online chess game (correspondence) and my rating did not go up. I have also joined ChessKid.com as part of my school's chess club, and won a few games on time there, with my rating staying at 600.
I just don't know if there is a reason for this occurring, possibly something to do with rating differences, or if it's a bug. Is anyone else having a similar problem?