Please help.

I don’t expect anyone to understand, but I’m 17, 5’3, and weigh 250 lbs. I’ve been bullied for a very big majority in my life and my parents are divorced. I was also diagnosed with cancer last year (papillary thyroid cancer) and my thyroid was removed. Which means I now have absolutely no metabolism and I have to take synthroid every day of my life so I don’t go into a coma— or worse, die.— I need to lose weight to be healthy again. I try so hard to go to the gym and to eat healthy but all I do is gain weight. My dosage rn for synthroid is 175mcg.