What Causes Craving Of Salt Post Knee Replacement Surgery?

i had a knee revision and emergency gall bladder surgery on Dec. 16th and emergency gall bladder on the 18th. I am a diabetic and they took me off of Metformin for 30 days. I had a knee replacement last year and developed staff infection in the knee out of no where in June, 2014. They removed the knee and I was without a knee for 6 months. They did the revision in Dec. I don't know what is going on, but I am craving salt.Can you please direct me in the right direction. I need to schedule an appointment with my primary care for blood work to re-start my diabetic medicine.