Uhm. I'm pretty sure just meat (and fish). Other than that, your body synthesizes its own.
I know that some (i.e. bodybuilders) do take it in the form of supplements - but taking high amounts of creatine in the forum of supplements is not without risks!!!
I would think if your doctor is suggesting that you get more of it - your doctor should be giving you the associated information on HOW to get it. As well as continuing to monitor you, to ensure you don't end up with issues resulting from taking too much.
Goal 1 - break 200 (46 pounds lost)**DONE**
Goal 2 - leave obesity behind (BMI 29.9, at 185#) **DONE**
Goal 3 - BMI = Normal (154# or less)
| current weight: 176.0