You very well might be eating too FEW calories. Women should NEVER EVER go below 1200 calories....and if you're at 185 pounds, 1200 is too few.....you could be caught in a starvation mode cycle....you can lose muscle mass, which means you burn even FEWER calories ever day, even sitting still.
Are you able to do anything that raises heart rate? My dad has had joint replacements, and the hardest thing is to do aerobic work outs. He's only recently been allowed back to biking, and his hip replacement was over a year ago. Getting the heart rate up can help a LOT with weight loss. Building muscle is very good, too, as you then burn more calories just sitting still.
I think you need to find a less condescending doctor
(just burns me up when they are like that), need to eat MORE calories in a day, and keep up with your rehab, as you'll be able to move more and more. Joint issues stink so bad - but you can get to the end of the tunnel.