Hey, you sound like me 2.5 years ago! Started at 172, and lost ~30lbs in 3 months. It is very doable, but it will take a little shake-up in the routine. Every says weight loss begins in the kitchen and ends at the gym and I couldn't agree more!
Starting by tackling the cola addiction is a great way to begin. That alone should reduce your calorie intake by a couple hundred (or more) calories. Lots of our ladies start with that one, then move on to the next dietary trouble spot. Beleive me, and about a million other users, logging your food will be an eye opener
. Use that information to see what you need to work on next.
I really hope you can find an exercise or activity that will amp up the number of calories you burn. Biking is a great one, BTW. And Zumba has gotten rave reviews, so keep it up.
Although my diet is now very good, I find that the difference between maintaining a dropping a few pounds is in the amount of aerobic exercise I get. When I am consistent 3 or 4 days a week I can drop a pound or 2 a week. When I slack off I don't tend to gain very much, but I sure don't lose no matter what my calorie intake is. But then again, I have a few years on you