Don't worry, you are going to have plateaus some times and then you will continue to lose weight. Right now your body is in a state of adjustment, your metabolism may be slowing a bit due to the decrease in caloric intake. You have lost 18 lbs., that is FABULOUS! Try not to be so hard on yourself. Remember, it is all about calories in versus calories out. Right now you are convalescing and not doing much just trying to let your body heal. When you are ready to become more active, it will start to come off a bit easier. Just let your body heal and when you are ready, get walking.
Best wishes.