How can I excercise if I can't stand up for more than a couple of minutes at a time?

I had a heart attack almost 2 yrs ago, been disabled for 21 yrs with possibly M.S., just recently diagnosed with Fibromyalga, and now I'm borderline diabetic.
I was always super thin growing up, then I gained some weight after having my youngest son, 23 yrs ago. It was a high risk pregnancy and I was confined to bed for the last 6 mos of my pregnancy. I was at least 45-50 lbs overweight up til I had my heart attack and had to quit smoking. Now I've totally ballooned and weigh close to 250 lbs. It just took everything in me to type that number. I can't tell my family, but I feel like I'm just waiting to die.
Does anyone else have any idea of what I'm going thru? My family tries to understand and support me, but they don't really understand.
Sandy