Do hydroceles grow if they aren't treated right away?

Possibly. Hydroceles can grow over time if left untreated. They may grow very slowly or more rapidly depending on the activity level of the patient.
Not necessarily. Many hydroceles in adults don't change size, some enlarge slowly. Hydroceles in infants can involute during first year of life, but an occasional one can enlarge rapidly and require surgery sooner rather than later. Best consult with a urologist.
Possibly. Most hydroceles reach a state of equilibrium where they neither grow or shrink. If your hydrocele continues to enlarge, see your md. You may have a hydrocele complicated by communication with the abdomen or an underlying problem with the testis or epididymis.