Postpartum weakness and fat loss.

I am 3.5 months postpartum after a C-section and exclusively breastfeeding. My pre-pregnancy weight was 56 kg, delivery weight was 73 kg, and current weight is 59.5 kg. Although I am still above my pre-pregnancy weight, I feel I have lost a lot of fat and muscle rapidly. My face and eyes look hollow and aged. I have significant fatigue, leg weakness, lower back pain, wrist pain, ankle joint pain, and body aches. During the first 45 days postpartum, I followed traditional “japa” diet restrictions and ate very little with limited food variety. Could this be due to nutritional deficiencies, anemia, thyroid issues, calcium/vitamin deficiency, or normal postpartum recovery with breastfeeding? What blood tests or investigations should I consider, and what dietary or supplement changes may help while continuing breastfeeding?