Is Surgery Necessary For A Thyroid Cyst Causing Pain When Swallowing?

Hi, I have a thyroidien kyste of 3.5 cm (left part of my throat) but these days it becomes inflamed and painful when I swallow food (only the left part of my throat is painful where the kyste is) is it necessary to make an operation? Is it obligatory to remove all the thyroid? (because the kyste is attached to the thyroid)? Or shall I live normal without any operation and stay under check up every 4 months? Thanks a lot.