transition to cow’s milk

I've just put my 1 year old onto cows milk a couple of weeks ago, and have only had 3 nights where he's slept through since then. Before then he generally slept through all the time. Anyone else have a similar problem? I was so excited that I didn't have to buy expensive formula anymore, but am thinking I'll have to put him back on it to see if it makes a diference. I don't know if it's the cow's milk unsettling him at night or if it's just a coincidence that I started the cows milk at the same time.