Hi there!
Having 21 and 23 year old sons who struggle to maintain their weight I can see where you're coming from.
First, I'm guessing you've probably reached a "plateau" in your weightloss. You've done a wonderful job of losing 20 pounds in two months! That's a great weightloss! Now your body is just saying "hold on buddy. Let me get used to this for a minute."
You didn't say what you are drinking instead of pop. If it's water, that's great. If it's juice or some other calorie ridden beverage, it might not be.
If you are drinking water, and you're drinking 6-8 glasses a day consistently, then shake it up a little. Drink 8 today, 9 tomorrow, and then 6 the next day. Sometimes that's enough to shake things up and break a plateau. If you're not drinking water at all...then START. At least 6 glasses a day.
Also, just a thought. 160 pounds for a guy of 5'9" is pretty darn close to what the charts say is "ideal". Your body may have just gotten to it's "right" size. Perhaps stepping up a strength training routine will help tone up the flabby areas and reduce the last little bit that you need to. Some weights or even the exercise bands might be a great addition to your walking routine.
Hope this helps. Good luck to you for becoming fit and healthy.