Under active thyroid

Hello everyone, I am 55 years old, female. I have an underactive thyroid, type two diabetes, mild fibromyalgia, psoriasis, irritable bowel syndrome, hiatus hernia, high blood pressure. In the last two years I have sprained my ankle (the left) 4 times, broken my arm (after a fall) and had a mini stroke. I desperately wanted to lose weight for 1st September when my daughter gets married but have only managed a few pounds. At the moment I weigh 262 pounds and would like to aim for 200 by January next year. Fingers crossed that I make it. Any suggestions? I try to walk my two dogs twice a week and exercise to the wii as many times a week as I can, but not every day or even as many as I would like.