Has your doctor done any tests to find out anything? Both cancer and diabetes can be confirmed/ruled out relatively easily with simply blood tests.
Have you had your thyroid checked to see if you might have hyperthyroidism? You need to get tested for TSH, Free T3 and Free T4. You should also get thyroid antibody tests to confirm/rule out both Hashimoto's Thyroiditis and Graves Disease, which are autoimmune thyroid diseases.
While Hashimoto's is, typically, associated with hypothyroidism and weight gain, it's often characterized by hyperthyroidism and weight loss in the early stages. Graves Disease is always associated with hyperthyroidism.