slc_melissa

Can you list out a few meals worth of foods?  Although some energy loss at the early stages seems normal, it sounds like yours is more extreme.  I'm wondering if you may not be eating enough.  It's really easy to accidentally go low carb. It's also easy to not eat enough fat to cover the accidental calorie gap.
Are you eating any sweet potatoes / potatoes / butternut squash kind of starch?  If not, I'd add those to 1-3 meals per day.  (Also, depending on female/male and where one is in the cycle, more starchy carbs can help.)
I agree with prepping meals, I don't get food boredom, so I like to make big batches of things (say, crockpot full of chili) that feeds me for 5+ meals.  And meals can be really basic and totally not instagram-worthy.  3 hard boiled eggs, a handful of olives, and a sweet potato I cooked in the microwave....takes minutes, covers all the bases.  Frozen veggies heated up with coconut milk and a can of salmon or chicken and few spices - super easy and I didn't even have to bust out a knife.

If you're eating nuts as your primary protein source, I think you'll be lacking a lot of protein. Nuts can be very hard on the digestive system, are recommended as a handful every other day at most, and don't have great omega 3/ omega 6 ratios. Anecdotally, nuts have been a factor in a lot of people's skin problems on the forum.

Please note that sugar free doesn't necessarily mean it's whole30 friendly, you still need to look at all the ingredients.

I like this soup for breakfast:
http://scooterandtrianglegirl.blogspot.com/2011/03/sweet-potato-kale-and-sausage-soup-this.html
If you're using pre-cooked sausage like I did, watch the ingredient list.  This made a really big batch.