I finished my first five games yesterday and have still not received any new games. Is there a problem with new game assignments?

No, there isn't.

You'll get a new one every 3 days regardless of how quickly you play.

Games are not assigned when you finishes ongoing games in the seasonal ladder. Rather they are assigned at specific times (think it's one new game every 4 days). You can check out a desription on the wiki

Edit: Beren you are too fast for me :P

Edited 7/16/2015 00:22:32

thanks, learn something new every day.