You definitely have polyhydramnios
It can be caused by maternal diabetes
, renal or other defects in the baby, due to placental diseases etc.
The most common cause is idiopathic, in which there is no reason found.
Your obstetrician can prescribe medication / suggest drawing some fluid out if the AFI crosses a critical level.
Meanwhile you are at risk of preterm labour, unstable lie of baby , malpresentation of baby, preterm rupture of membranes
, cord prolapse of baby and other complications.
Please strictly adhere to the medical advice
given to you, and have thorough scanning of baby for abnormalities.