In some cases one lobe can be larger then other due to the nodule, and the ultrasound should should determine if that lobe has nodule or if the doctor just palpated it wrong (it is quite common).
The AACE recommended thyroid neck check self exam can can help catch the nodule or swelling right away.
If you have swelling of the thyroid gland then yes there is something not quite right,more than likely you have a goiter. A scans a good thing to see what may be causing this. It is conman for a goiter to be bought on by hashimoto disease or Graves disease. (A scan will also check for noduals on the gland, dont panic though as this is also common). which is antibodies attacking the gland. also have they done the blood tests to check how your thyroid levels are..