I have a transplant kidney. My CMV test is positive. I used ganciclovir for 14 days, but what does it do?

Needs clarification. If your CMV antibody (IgG) test was (+), it indicates that you had a prior exposure to the virus but does not mean an active infection. In most renal transplant recipients, anti-viral medication is usually given to prevent CMV reactivation. If your blood PCR test was (+) for CMV, it indicates active presence of the virus in the blood and its tx requires ganciclovir (IV) or valganciclovir (oral).
What is positive? It depends what CMV test is positive. If the donor or your igg antibody test is positive it means past exposure. Recipients are often given 14 days of IV Ganciclovir to prevent reactivation. If you are growing the virus in your blood after transplant it should be treated. Most commonly the oral nucleoside inhibitor valganciclovir or IV Ganciclovir is used.