I am just like you. And, I am now walking 3 miles five times a week. In an hour or less per walk. If anyone told me a month ago I would be walking fifteen miles a week, I'd have called them a straight up liar. I can't diet. But, I can do my darndest to choose to make a healthy decision about whatever I'm about to eat. I did choose to drink only water, ok, I have one coffee with some coffeemate and a tap of sugar at work. But I drink 9 glasses of water a day. And, I am amazed at how big a difference just being well hydrated makes!
U can start from right where u r. In fact, how u feel right now is a perfect starting point. U will only improve from here! Even if you just walk for five minutes, that's more than u walked yesterday. It's free and it does get easier. When I started....just a month ago......I could barely handle a mile. Had to stop half a dozen times. Now I walk without needing to stop. I have less back pain. It helps relieve daily stress.
So much inspiration is available here. Please know u r not alone. We believe in you!