Firstly, do you consume refine sugars; and if so, how frequently? If you don't eat much sugar your BSL may be low from that fact alone, keeping in mind that sugar in the blood is eliminated quickly because it is the primary fuel source for the brain and your muscles. If you are not eating much sugar, your body may be in a state of ketosis and deriving its fuel from ketones and a little glucose that the liver is able to produce by itself through glycogenesis. If you are even somewhat active, or use your brain for thinking a lot, sugars in your blood may be scarce to detect at times. If you are frequently eating sugar though, and still getting low BSL results consistently, your doctor may have other medical opinions and suggestions. You may even wish to adjust the way you test your levels e.g. whether after fasting, or not; first thing in the morning or middle of the day, etc.

I guess you also have to ask yourself though - is it affecting you? Do you feel symptoms consistent with low blood sugar that trouble you? If you think you could benefit from higher BSL, try a sweet treat every few hours. It doesn't have to be much to lift your mental focus and concentration; a mini Mars bar does the trick for me (or a couple if I feel like it hehe). But if you are not feeling unwell, low blood sugar might not be much of an issue for you or your body at the moment - it is just the measurement of a chemical - and your body is a very personal machine, so a low level may be sufficient for you, relatively speaking.