pressure behind your eyes and a swollen thyroid gland sounds to me like you have hyperthyroid - you may want to get that checked by a doctor.
I had hyperthyroid when I was 18 and my thyroid gland was enlarged, and there was pressure behind my eyes to the point that my eyes started to bulge out a bit. The doctors treated it by dissolving my thyroid with nuclear Iodine ( I-131) and have since been hypothyroid.
If you have hyperthyroid, I would encourage you to do as much research as possible and not be like I was when I was 18 ( blindly following doctors recommendations)