I had a thyroid ultrasound at the endocrinologist and he saw 3 nodules. is cancer usually 1 nodule?

Not always: Certainly, cancer is less common with multiple nodules, but not unheard of. The endocrinologist can tell you if any of the nodules are suspicious enough to warrant biopsy.

Not necessarily: Multiple nodules may represent a goiter. If they are 1 cm or larger, have specks of calcium, or otherwise look concerning, should have an fna (fine needle aspiration biopsy) to look at the cells and determine if benign or cancerous. Thryroid function tests are useful too. Occasionally radioiodine scan can help determine if nodules or the gland is overactive.