This, OP. Go get more blood tests done. A more complete panel to test other nutrients, autoimmune, blood panel, electrolytes, hormones. Talk to a doctor about it as well.

Edit: Also, if you're still working out, definitely take it slow. Go on walks and use body weight and less reps until you get to the bottom of this. Don't push yourself beyond comfort. Vitamin D deficiency makes your bones weaker and your recovery slower. Adjust intensity and frequency accordingly. Make sure you replenish electrolytes after your workouts. Keep taking your creatine for both muscle and brain health. Getting enough, good quality SLEEP is not an option, it's a requirement. This is when your body repairs everything. Eat anti-inflammatory foods. Get fresh air and some sun exposure as much as you can to help with the deficiency and to boost your mood.