Honestly I probably wouldn't be going out on a limb to say it was the Cedar. It's highly toxic, yes pine is too, but Cedar is much stronger!

If you want to cut back on the smell you could mix your pine with the recycled paper bedding. It's safe and it really helps with the smell. I notice that I have to change my breeder rat cages (pine) twice as often as my pet rat cage (recycled paper).