Hi Lena,
I am still not particularly worried about anything here,
The echogenic area could still be a bit of thymus,
Or some fat,
Another thought: did you think on your first image that the right lobe of thyroid is less echogenic than the left? or was it just projectional?
If you have a thyroiditis in the earlier stages it may affect one lobe a lot more than the other and it is a patchy process. In cases like this normal thyroid tissue that is yet to be affected looks echogenic against the background of the thyroiditis which makes the thyroid tissue look hypo echoic.
Steve
If you have some more images I would gladly take a look.