You already know the answer to this question - you need to go and see your GP. It would be useful to know your age and BMI. Diabetes is split into 2 main sorts -

Type 1 which is when your pancreas stops making insulin this tends to affect younger adults and children and your weight is irrelevant. It happens very quickly and you becomes very ill very quickly.

Type 2 which is when your insulin is no longer effective. It affects older people and mainly affects overweight people, the more you weigh the more likely you are to get it. It also runs in families. The symptoms come on slowly and at first may only be tiredness. Then people drink more and pee more, if untreated they will start to lose weight. This sounds more like your symptoms.

The best test is a fasting blood glucose (nothing to eat from midnight the night before the test)

In other words go see your GP!