I too am not familiar with you medical conditions. However, one thing that caught my attention was the 150-170 heart rate that you mention. That is WAY too high for optimal fat burning at your age & resting heart rate. You should be targeting closer to 135-145. Anything higher than that stars burning more carbohydrates as fuel; and you are interested in burning fat.
Also, as brightstar suggested, use that muscle mass to your fat burning advantage. It is much easier to loose fat when you are muscular. And it is much easier to loose muscle than it is fat.
Check out these articles & good luck!