Diarrhea is common gastrointestinal problem in diabetic patients.
If you take metformin, than the diarrhea can be side effect of this drug.
If you are insulin dependent, the diet, the changes in bowels, use of artificial sweeteners all contribute for the diabetic diarrhea to occur.
Your inability to control the bowels is known as fecal incontinence. There are probably few factors in your case that are causing this disorder.
First cause is diarrhea. It is far more difficult to control the loose stool that fills the rectum at a faster rate (Even people who don’t have fecal incontinence can leak stool when they have diarrhea. Actually, chronic diarrhea leads to hemorrhoids, that cause you painful anus and incomplete closer of anal opening because of internal hemorrhoids, that results in stool leakage. It is very possible that this is what you are experiencing. The long-time diarrhea and hemorrhoids can also cause rectal prolapse, and its symptom is fecal incontinence).
Another thing that may cause fecal incontinence in diabetic patient is nerve damage that occurs with time due to hyperglycemia.

Visit your physician!