Hi, I'm sorry that I can't type in Chinese, but hopefully I can answer to your question.
Basically, diabetes is classified in 3 main categories: type 1 (insulin dependent diabetes IDD), type 2 (non-insulin dependent diabetes NIDD), and gestational diabetes.
In type 1, the pancreas can't produce or not produce at all insulin (hormone signals body cells to pick up blood sugar as energy). In type 2, insulin is made but it becomes resistant to the body cells (or less sensitive to the cells). In both cases, blood sugars accumulate in the body; thus the body blood sugars become high throughout the day. Type one is usually related to genetic, whereas type 2 is more related to overweight and obesity.
Syptoms of high blood sugar (hyperglycemia) are frequent thirst, urination, dizziness. And in long term, chronic high blood sugar increases risk of heart disease.
Anyway, the information I mention above is only to describe the disease itself. It might not related to your case.
As you said, you are only 15, thin, but have a family history of diabetes. Honesty, the symptoms you wrote are quite vague. To know if you are diabetes or not, the only solution is to see your family doctor, ask him or her to prescribe you a blood test.
Usually, if it's the first time you check your blood glucose, they usually ask you to fast (not eat for about 12 hrs), and normally you should be around 4-7mmol/L for blood glucose. However, if you are higher than this range, you might need to do a second test, which might require you to drink something like an orange juice, then you wait for about 1-2 hours.
What I suggest you now is to not worried that much. If you are really in concern, go to see the doctor and ask to do the blood test as I descripted earlier.
Good luck! :)
2009-01-02 13:53:10 補充:
sorry i forget to mention that other than checking blood glucose from the blood test, Ha1C (hemoglobin which reflects your blood glucose level for the last 6-7 months) will be also checked too.