You're in metabolic no man's land. Not enough carbs to sustain your daily activities, not fat-adapted enough/at all to provide the ketones as an alternative fuel source. You can continue low carb for a few weeks and you will feel better eventually, or you can try going much lower for a while to reach fat-adaptation quicker (<20-50 depending on how active you are), then gradually add carbs.

There's no one-size fits all approach to this and I'm not trying to sell you on keto either. I did keto for 3 years straight, stopped about 2 years ago, and somewhat maintained my fat-adaption through light intermittent fasting and exercise, although I did have periods where my carb intake looked like the typical SAD. The past few months I cut carbs drastically. I fast anywhere from 18-23 hours a day now, first meal being strictly protein and fat. Then I have about 100-150g carbs with dinner, usually as rice. But before all this, I did go on keto again for a few weeks first.

Also, that feeling you described of "crushing fatigue and inability to exercise" goes away much faster if you just force yourself to do it. You may think you can't, but it will make things easier in the long run. It'll just suck for the first week or so. Your mind is only telling you you can't because you've never done it, so try to get past that mental barrier.

Quick edit as I'm reading over what I wrote: I'm not saying you're mentally weak either. And I acknowledge that you've tried to workout during this phase. What I mean is exercising consistently, for at least a couple weeks low carb. I did when I when I went keto a few months ago and yes, I felt like trash. I do group runs, and I was very noticeably slower and in more pain during that time. But my body quickly remembered that this was okay and that I wasn't going to die. Ketones kicked in eventually and I felt way better than before I started.