Hi,
The two most common causes of hyperthyroidism are Graves' disease and toxic multinodular (TMG). The scan would show if nodules were the cause. In the absence of nodules, and with an increased uptake, Graves' disease is considered the likely cause of hyperthyroidism. Graves' can't really be confirmed though without tests for thyroid antibodies.
Diet makes a huge difference in Graves' disease. It really is difficult to afford processed foods when you're working but with some planning you can cut back on them by bringing fresh fruit or vegetables. If you typically eat out, you can opt for salads with grilled chicken. You'll want to indefinitely avoid excess iodine in processed and dairy foods, but even small changes help. If you're forced to eat some fast and processed foods for one meal you can make up for it by being more careful with your other meals.
Best, Elaine