I'd be a little patient as your doctor adviced. He/she seems to have much more info to give you if the steriod fails. You may not have RSD and the doctor is siding with a bit of caution. You are correct in that if it is truly RSD agressive treatment may put it in remission in its early stages. I'm no doctor nor do I have RSD but my wife does and has for several years with no treatment the first 4 years. If it were me I'd relax as much as you can, keep stress to a minimum, wait out the month on the steriod. Also if it were me in the mean time I'd look at water thearapy if possible, a warm pool to lift some gravity away from the injured area.
Good luck and hopefully everything will turn out fine!

jim