My dogs throws up randomly

Hi,  I have a German shepard and a German shepard/ Husky mix (both 4 years old).  I've just changed my dogs over to raw feeding less than 6 months ago.  I've only been feeding them boneless chicken as that is the easiest and cheapest for me.  Sometimes they'd get giblets, livers, eggs, and yogurt (not all together).  

Within the last month both of my dogs have been throwing up in the mornings.  Not every morning, just once in a while.  So far 3 times each dog (they alternate on who gets to puke that day).  At first I thought maybe it's because they just came back from a very tiring walk (it's hot in California) and ate right away, so after the first time, I wait an hour after the walk to feed them.  

Then it happened again, this time they ate and played hard right after and then puked (it's hard to stop them from playing when they want to play).  So now I watch them after they eat.  The last few times, they would just puke for no reason (or so I think).  I did run out of yogurt and kept forgetting to buy more.  

Do you think it's because there was no yogurt?  Or is it something else?  I just bought some today, so I'm giving it to them again, but I just want to make sure.  Thanks a bunch!