Is my thyroid nodule "fast growing" and cancerous?

Could be: Rapid growth of known thyroid nodule could be malignant, or bleed into the nodule, see your doctor to find the cause ( and to treat).

Not necessarily: Most thyorid noduels are benign e.g. Thyroid cyst, goitre. If one is concerned, ultrasound is necessary to distinguish a solid one from a cystic one. If necessary, a fine needle biopsy may be indicated depending on the suspicions. Change in size of nodule may not be a reflection it's cancerous.

Maybe: All thyroid nodules should be considered ca until proven otherwise. That said benign thyroid nodules are very common.