19 Year-old Would Develop Diabetes?

Over the past few weeks I ve been very tired, struggling to stay awake for more than about 12 hours per day. I ve also been very very thirsty despite drinking almost constantly, and I ve been feeling dizzy like I might fall over or faint after eating or drinking sugary things. I know these can be symptoms of diabetes, but how likely is it that a 19 year old would develop diabetes? I m otherwise healthy, and am well within the healthy BMI scales... I ll make a doctors appointment when I get a chance, but I was just wondering what the likelihood was. My Dad was diagnosed with diabetes when he was about 50, and my grandmother was diagnosed when she was about 80... I m just drinking water. Probably about 4/5 litres a day since I ve been feeling like this. I dont really drink anything else, a glass of milk every couple of days and a mug of hot chocolate once a week or so... I dont eat a lot of sugar, I tend to be quite healthy.