One of the reasons diets don't work very well is that "starving yourself" is unpleasant and creates an emotional feeling of deprivation, as well as changing your metabolism to make weight loss less likely.
Weight control is a lifestyle decision. Weight is actually very simple . . . if you eat more than you burn off, you gain weight. Weight loss requires reducing the intake and increasing the outgo. In your case, you're going to have to be creative to increase the outgo, because of the recent surgery, but swimming is luckily a non-weight-bearing activity which is inefficient and therefore burns a fair amount of energy. Water aerobics programs are good for the joint-impaired, as well.
One of the keys is not to say, "I'm going to lose all the weight I want to lose in the next 7 months." It's not going to happen, most likely. So you do it in increments.
Little things -- Park at the far end of the lot; walk the last flight of stairs to where you're going. Use a push mower on the lawn. Sweep your floor instead of vacuuming it. Make things a little MORE work.
Eating . . . Become aware. Think about what you put in your mouth. One of my rules is not to drink things with calories (which I break for wine with dinner). That's an easy place to cut out a lot of calories, if you drink sodas or juices or even much milk. Cut portions -- start with half of what you think you want. Eat that (and eat slowly) and wait twenty or thirty minutes before you give yourself a second helping -- and don't take the second helping if you can avoid it. It can be amazing how little food is actually required to feel replete, if you give your body time to recognize it's there.
It can also be very helpful to break the day's intake up into a bunch of small meals, rather than three large ones. That way, you don't get ravenously hungry before you give yourself access to food.
And, at least for me, the saddest fact is that, to control my intake well, I have to avoid the foods I love so much that I'm helpless before them . . . which means bread and pasta. Those are treats, but not a staple part of my diet. I'm also really careful to be sure that we don't have truly evil things (chips, crackers, cookies, ice cream) in our house. If you want to snack in our house, you have to put some work into it, and at some point in the process, you're likely to remember that you aren't supposed to be doing that
It really is a lifestyle decision. You have to look at what you were doing that caused the weight gain, and figure out how to reverse it. And, like controlling addictions, it only works if you are really sincere with yourself about wanting to change.
