Hypothyroidism: This condition is a common cause of postpartum joint pain, lethargy, and weight gain, especially in the context of a recent pregnancy or abortion. The stress of pregnancy can sometimes trigger autoimmune thyroiditis, leading to hypothyroidism.

Postpartum Depression: While not directly causing joint pain, postpartum depression can lead to lethargy and weight changes. The history of abortion might also contribute to psychological distress.
Fibromyalgia: This chronic condition can be exacerbated by the physical and emotional stress of pregnancy and abortion, leading to widespread joint pain and fatigue.
Polycystic Ovary Syndrome (PCOS): Weight gain and lethargy could be related to PCOS, especially if there are other symptoms like irregular menstrual cycles or signs of hyperandrogenism.

Addison's Disease: Although rare, Addison's disease (primary adrenal insufficiency) can cause fatigue, weight gain, and joint pain. It's crucial to consider this diagnosis due to its potential severity and the need for prompt treatment.
Lupus: Systemic lupus erythematosus can be triggered by pregnancy and cause a variety of symptoms including joint pain, fatigue, and weight changes. Missing this diagnosis could lead to significant morbidity.

Sheehan Syndrome: A rare but potentially life-threatening condition caused by postpartum necrosis of the pituitary gland, leading to hypopituitarism. Symptoms can include fatigue, weight gain, and potentially joint pain due to associated endocrine deficiencies.
Postpartum Thyroiditis: An inflammatory condition of the thyroid gland that can occur after pregnancy, leading to transient hyperthyroidism followed by hypothyroidism. It might cause joint pain, lethargy, and weight changes, among other symptoms.