What Causes Recurrent Cellulitis?

I'm trying to figure out why I have gotten cellulitis for the 2nd time this year. My doctor did a cbc and it was ok. I work 12 hr. shifts and was wondering if being on my feet so much might have something to do with it. Also, I'm diabetic and have had CABG x4 5yrs ago and it the leg that they harvested from.