Welcome to the forum first off,

I can't really sympathize to your situation of the being the only overweight person. But I understand being overweight, non the less. For a majority of overweight people, their weight gain is out of their hands. There are so many medical factors that could be the cause, underactive thyroid, slow metabolism, intollerance to insulin, etc. A lot of people that have been thin all their life are ignorant to those conditions and feel that being fat is a personal decision, when its not. You may feel alone in your family but you are not alone here at the lowcarber forum

I'm glad that you want to exercise. Start off slowly. You have the right idea. No need to come out of the gate running right away. You can work up to that if that's your goal. Add 5 minutes to your walking time every week until you can do an hour and go faster than 2.5mph. From someone that hates working out, trust me, it gets easier.

We will be here for you. I"m glad you decided to make a change in your lifestyle.