A.F.
Both of my kids and my husband have Type 1 diabetes. Absolutely no one in the family has ever had it before my husband. Type 1 is not typically handed down through generations like type 2. Type 1 diabetes is an auto-immune disease and does not need a genetic factor to manifest.
Absolutely make an appointment with your doctor. Excessive thirst, frequent urination, headaches are all symptoms of high blood sugars.
Your son does not need to fast to be tested for diabetes. They will do a blood draw and a urine sample. They will test the blood glucose levels and look for ketones in the urine, among other things.
In response to a poster below.....my daughter was diagnosed with diabetes at age 19 months and frequent urination and excessive thirst were the ONLY symptoms that she had.
I really, really, really hope that your son doesn't have diabetes. But, I think you are doing the right thing by checking it out!
Please let us know how everything goes!