You need to see your Doctor. They will have a lab analyze your blood and they will tell you if you are Diabetic. If you are just asking for some symptoms of low blood sugar, I can tell you how I know if my sugar level is low. I'll get light headed, get shakes in my hands, sweat, blurred vision, extremely thirsty and spasms in my legs.
See your doctor about having a fasting blood glucose test. They'll give you specific instructions about what and when you're allowed to eat before the blood draw. You'll be notified of the analysis results.
Let us postulate that 'normal' blood sugar level is 100mg/deciliter. As your glucose level falls you may feel cold and/or get a mild headache. At perhaps 80mg/dl you may start sweating even though cold and you may start trembling which is especially notable in your hands. As your glucose level continues to drop you may feel very 'weak' and extraordinarily hungry. If you drop below 70mg/dl you should go to a hospital. You should not drive or use machinery, or ride a bicycle, as you may pass out. Low blood sugar may also cause you to be irritable or 'ill tempered'. Symptoms vary and the blood sugar level that triggers those symptoms may vary from person to person and depend on tolerance. Recovery from levels below 70mg/dl may take hours or even a day. Obviously one should not allow levels to get so low. eat something with starch and protean before you feel awful. I do not recommend candy or sugar which may cause a rebound and make your condition worse. However, in an emergency eat what you can and get to a hospital.
It is easy to tell because you run out of energy, can't focus, have blurry vision, become irritable and often feel faint. After eating something you will feel normal again. If not, it may be something else.
I work at a Diabetes Ed Center. Low Blood Glucose comes from not enough food, more activity than you are used to doing, or medication error. First step is to self monitor your blood glucose. If you are 70mg/dl or below, treat with a fast acting Carbohydrate (juice, soda, glucose tabs, etc). Symptoms come on all of a sudden. Common symptoms include shakiness, sweating, nervousness, etc. It would be helpful to talk with your doctor regarding treatment of your diabetes or get a diagnosis to find out if you have diabetes.