There are many different things that cause the symptoms you describe, and low blood sugar is certainly one of them. Anemia
(low red blood cell count), infection, or hormonal imbalance (especially with thyroid hormone) can also cause a weak and shaky feeling. To help determine what is causing you to feel this way, the best thing for you to do is to see your primary care doctor
for a detailed history and exam. Your health history can sometimes be very helpful. For example, people with a family history of endocrine disease may be more likely to have a problem with their thyroid. Women who are having regular menstrual cycles can often be chronically anemic. In addition, it will be important for your doctor to know about any other symptoms you have noticed. Are you also having fevers, cough, any abdominal discomfort, or weight loss
? Often it is the other associated symptoms a person does or does not have that can help suggest what the underlying issue might be. Finally, your doctor will definitely want to do a basic physical exam looking for anything different from your last exam or that is unusual (swollen lymph nodes, or an enlarged thyroid, for example). Basic blood work will also likely be a part of your visit. Hopefully you and your doctor can work together to figure out what is making you feel this way!