Would a doctor only request a biopsy if something looked suspicious on ultrasound? Never had 2nd usound to check if shrink/grow (lymph node and cyst)

Precaution. Sometimes a doctor requests a repeat study in radiology or a biopsy just as a precaution to be sure the condition is benign. Many cysts are a benign condition, but I do not know where your lymph node & cyst are located. Best thing is for you to ask your doctor WHY are these being ordered for you.