Hello, Lyn. Belated welcome to a great forum. Visiting here often will be one of your best strategies for sticking with your new way of eating. The first thing to learn: every BODY is different. Comparing your experience to reports from others can be discouraging, as you've noticed. Don't do that.

Second, three weeks is not very long in nutritional terms. Your body will take its time adjusting to the new plan. I ditto what someone else said: eating only one meal a day as you are accustomed to is actually a pretty good habit. Just make sure to eat enough, and eat on plan. Don't let yourself get hungry.

Finally, bear in mind that you are not on a "diet." SBD (or Low-carb or Keto or LCHF or Atkins, etc.) are simply names for a healthy way of eating that eliminates massive amounts of sugar, starch, and nutritionally unhelpful foods from your life. And that's for life.

Best wishes!