Lose 50lbs

I'm 210lbs and stand at 5'9. I've grown uncomfortable with my weight as I've gained quite a bit over the last 2 years. I have suspected hypothrodism, so that plays a part in this. I'm vegan but I have troubles with portion control and not eating the right things. Also excercising. It's so incredibly hot here that I can't step outside without suffocating, and my house doesn't have ac. I try to go for walks but they're not very long. 

Any tips on motivation and how to control myself? 

Thanks!!