You're supposed to have proof of origin but if it was bought from a pet shop here then you probably don't have one.

You need to go to the CITES office in the Ministry of Environment (as is typical with government offices, they don't answer their phones!) and ask for one there. If you explain the situation and tell them where you got him from and how long you've had him they should give you one. It's also advisable to have a health certificate from your vet which normally helps with the CITES certificate application.