Good for you and keep up the good work! I'm impressed with what you are able to do right now! I too would also recommend the Couch to 5K program mentioned below. I am doing it now (albeit very slowly) and am now in week 7 and am jogging 25 minutes at a time. In the beginning you walk for 5 minutes to warm up, then only jog for 30 seconds, then walk 90 seconds and alternate again and again until it's time to cool down. Workouts are 25-35 minutes long. It's a great way to get started and not injure yourself, and having a specific plan and goals to reach will keep you from burning out.
Interval cardio (which couch to 5K does in the beginning) has proven to be a more effective way to burn calories and lose weight than just keeping the same pace in a workout, so it is actually great to get your heart rate up, then recover a bit, then get it up again repeatedly. My beginner interval cardio workout on a treadmill used to look like this:
Warm up at 3.0 mph for 2 minutes
3.5 mph for 1 minute
4.0 mph for 1 minute
4.5 mph for 1 minute
5.0 mph for 1 minute (this is my jogging pace)
Repeat the 3.5 - 5.0 steps 3 more times (you'll be at 18 minutes), then go one more minute at 5.0 mph and then drop down to 3.0 for the last minute.
I find that training for an event is a great way to keep me focused and on track. I would highly encourage you to recruit a friend (maybe a co-worker who is also trying to get healther?) and sign up for a 5K race in early spring. A 5K is a doable goal for a beginner and in most races, there are a few people who walk part of the way so you don't have to worry about being the only beginner. I can't actually run the whole way yet (I hope to by next month because I have another race in November...just need to get 10 more minutes!) but I've done two 5Ks, a sprint triathlon and a 10K.
Again...congrats on the changes you are making and keep it up!