total thyroidectomy and weight gain

I had a total thyroidectomy in 2000 and have steadily put on weight. I take .175 synthroid daily. I have watched calories, added exercise, even hired a personal trainer and continue to gain weight. The medical professionals have no mercy and say it is due to my age and eating habits. I cut my caloric intake to 1350 a day and increased workout time to 1/2 hour of walking and 1/2 of bicycling and GAINED weight. It is frustrating. Sure wish I had an answer.