You're doing exactly the right thing. When you're stuck, shake things up! Soon you'll need to do more than walking though, and don't forget that building muscle is very important in speeding up your metabolism. You may gain weight initially, but it will be muscle and you'll be a smaller size.
Our fight with weightloss is a result of our bodies' tendency to reach homeostasis or set point. You have to constantly challenge your body, change up your eating patterns, and fool it into thinking you're not starving. I also found that eating 6 small meals a day instead of 3 bigger ones helps fool my system, and I'm also less hungry on the same amount (or less) of food.
I started off 220 pounds (31 BMI) and slow walking. That worked for 5 months. But now at 163 I have to run intervals and lift weights to see any change. I don't mind though, now I'm a competitive athlete and I won the masters division last Saturday in a 5K race! Woo! Two years ago I couldn't run 1/4 mile.