Hi jamiti,
Thanks for writing and welcome to the ali fitness forum. I am sorry to hear that you've had such a difficult surgery, but am very glad to hear that you've come through it successfully!
To address your question, our bodies are continually burning calories all throughout the day, even at rest. The amount of calories that you are burning varies with the amount of activity that you're doing (rest vs. activity), as well as other physiological factors, such as metabolism, your height, weight, and current fitness level. It sounds as if you're doing all that you can do exercise-wise! Working out 45 minutes to an hour+ per session is definitely burning a good amount of calories and is strengthening and enabling your back for a full recovery.
Stay the course and take it day by day! Give your body the time for a full recovery so that you can increase the amount and intensity of your workouts when you are healthy!
With the help of alli, a healthy, low-fat diet and your PT, you should still see positive results!
Your friend in fitness,
Kelli