If you're cutting back to 50g from a standard American diet, this is a huge change. Your body is searching for its typical sugar/carb energy source and not finding it, so its signaling to you that it needs food. This happens to a lot of people. Just keep eating protein and fat and stick to the carb limits on your plan. Don't worry about it for the first week or two.

As you go forward, try to eat a lot at meals so you can cut back on "on day long" snacking. Even if you're making low carb choices, this can keep spiking your insulin, which you want to avoid.

First day--you're doing great!