tears have nasty odor

I recently had to change Sunny's diet and he is now on Hills prescription diet Kd. He tears a lot, which he always has, but it seems moreso now and it smells bad -- real bad. It is like a moldy smell. The new diet didn't really start this, but it definitely has increased since the change. Any ideas how to deal with this. I wash his face but it doesn't dry and the next thing you know it smells bad again. He is 7 mos. and probably teething a bit still.