Things to consider & discuss with your doctor:
Parasites, leaky gut (L-glutamine may help), essential fatty acids supplements (Omega 3, 6, 9 ~ flaxseed meal and fish oil are best sources), digestive enzymes, inflammation in the bowel secondary to Lyme/coinfections, other food allergies/intolerances, NutriGenomics, Adrenal and Thyroid hormone anomalies (possibly even subclinical hyperthyroid), Diabetes (can cause weight loss)...
Also, if you are eating a ketogenic diet (ketones can be seen in urine if this is happening), your body may be devouring your muscle tissue for sugar. Might need to include some complex carbs if you can to help offset this.
Could also be another metabolic issue; organic acids urine test, stool study (Genova has a good comprehensive study), and/or nutrigenomics test (genetic variant expression affecting methylation & related metabolic enzyme cycles in the liver/mitochondria) may yield additional good info.
I hope this helps - good luck,
Chronic Lyme Disease, Chronic Bartonella (clinical dx only), Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, chronic Lymphopenia, etc.; G-Tube; Currently trying to wean off TPN.
Meds: Pulmicort, IV Ceftazidime, Heparin (to flush PICC line), Claritin, Domperidone, Colloidal Silver (used topically), probiotics, Milk Thistle, Ailanthus, homeopathy.