As a diabetic, you probably are, or at some point in your life will have a problem with water retention. Creatine can be a slippery slope if used incorrectly for everybody, much less a person in your condition. Use creatine ethyl ester like Prince suggests, pre workout. Stay away from creatine monohydrate as it will more likely cause you to retain water.
NOTE::: when you start using creatine, you will need to start drinking almost twice as much water as you are now. The presence of creatine supplementation in the body mimics the same response as sodium. This will stress out your thyroid and adrenals and cause you to become imbalanced hormonally (especially as a diabetic because your hormonal glands are already overburdened). When those glands become stressed they secrete an acid that is actually toxic to the body and can cause you to feel very lethargic. It's your body's way of trying to tell you to take it easy. Prevent this from happening by drinking your bodyweight in ounces of water a day. Loose weight, gain muscle, use less insulin and feel great. Best of luck to you!