Incidental thyroid nodule found measuring 7mm hypoechoic.1 month later thyroid specialist said there was no nodule. do i need another u/s?if so, when?

Not necessarily: A 7 mm thyroid nodule is considered well under the 1 cm size at which we start to be more concerned. The endocrinologist didn't even see one when you followed up. I would not recommend any planned follow up with imaging. Other favors are important like your family history of thyroid problems, exposure to ionizing radiation, thyroid function tests, & thyroid antibodies. Ask endocrinologist.