Depending on factors like your muscle % and your bone density, a BMI of 19.5 is still healthy, but on the lower end. Maybe you should work on toning muscles, instead of losing weight. Losing any more weight may be dangerous, and you can get much better results by doing the right kind of exercises.

I would recommend that you do cardio exercises for about half an hour each day, and then do some muscle training for another half an hour to tone your body. You will see much better results that way, than just walking for hours on end.

Remember – its always important to talk to your doctor before you go on any type of exercise program, as he or she will be able to guide you and determine what types of exercises are best for you.
References :

Nothing works, besides dedication and intelligence towards the subject of losing weight.

First, depending on how much weight you need to lose, your diet is the first concern. You can’t eat 10,000 calories a day and expect the weight to come off, even if you are exercising a lot. Which brings us to the next thing. Duh, Exercising…

This is a must especially if you need to a lot of weight. Get at least 30 mins of some good hardcore exercising. Do some cardio, in the long run, it’s good for the heart.

However, I find the most hardest part of losing weight/keeping it off, in my diet. It’s so hard to keep your fingers out of the cookie jar or those chocolate goodies. I’ve found a great addition to help any one out, it’s a natural weight loss supplement called Proactol. Now don’t get all crazy on me and say diet pills don’t work. That is true, but not in this case. This one isn’t meant to burn pounds while you sit on the couch. It’s an appetite suppressant, along with being a fat binder. I saved money on the pills at theweightlossplace dot com along with getting some good info. It basically makes those fingers not go towards the cookie jar. For me it’s the best pill I’ve tried and I’ve tried cupboards full. Now this doesn’t mean you have to follow my foot steps but I’ve successfully lost roughly 70 pounds and keeping it off til this day.

Well good luck and remember what I said, Dedicate.
References :