At your weight it's probably moot whether cardio or weights is better. Just walking is a weight workout for you, I imagine. I also guess it is difficult for you to get your heart rate very high while on the treadmill. A slow pace on a treadmill burns a higher percentage of fat calories than any other exercise.

You are burning tremendous amount of calories just walking on a treadmill. The only reason for weights is to build muscle mass so that you are burning more calories while doing cardio. So stick with cardio for now.

The Adkins diet will make you lose weight faster than any other diet and it works without chemical help.