I was the same until I moved and we now live on a farm. I go for a walk nearly everyday and you are right it is not easy to stay motivated but I found walking the dogs a good reason.
Also (and This may sound stupied) using like a star chart system so if you walk 5 out of 7 days then you get a reward. It doesn't have to be expensive your fourite dinner or TV programe or treat, movie, a bubble bath.
I found that I lost my weight really slowly that I didn't really notice. I do have to watch the chocolate though.
In the nearest town there is a group that is called strollersize and once a week or month they meet at a local park and walk. Maybe if you live in a town or city there maybe a group like that or you caould start one up.
Keep up the good work guys
Tineka, Mum to Hamish 3yrs, Abby 1yr & 1due 10/04