There's only one thyroid - not two. You need to have testing.
Your thyroid has 2 lobes and an isthmus. Have you had it completely removed? Can you be more specific with your question?
Many of us have multiple nodules, but don't need our thyroid removed.
You know, sometimes things just happen. Since you had breast cancer then had to have your thyroid out, it doesn't mean both are related to each other.
Sometimes it works the other way around, people with thyroid cancer can then go on to develop cancers elsewhere. Even though they may be elsewhere, say in the breast, they are referred to as Thyroid Cancer due to the cells which are most apparent in that area.
For you it may well just be coincidence.
I wish you well.