As far as I know, you must do the exam now. Before, US licenses could be swapped without the exam, but it changed about a year ago or so. However, you may be able to obtain a temporary license, which can be renewed every 3 months, provided you have an "international driver's license" ! and that allows you to drive rentals only. search for "qatar temporary license" it will direct you to Hukoomi website for e-gov details about it.