It is common to gain weight after a major surgery like hysterectomy. Mostly because we become more sedentary initially because of pain and then because we are deconditioned.
A couple of suggestions:
Get your thyroid hormone level checked if not done recently. Talk to your doctor about changing you from atenolol to an ace inhibitor for your blood pressure. Some patients develop lethargy on beta-blockers.
Most importantly, make up your mind to lose weight. The basic principle of weight gain is that if one consumes more calories than you burn,the extra calories get stored as fat and thus the extra weight. Start paying attention to what you are eating. You may even consider going to a nutritionist to come up with a 1200 calorie meal plan for you.
The second thing is burning calories. You need to start some sort of aerobic exercise. Do not look for a reason not to do it, but find ways to start doing. You may start a walking program with you co-workers during recess, or evening walks with your spouse or neighbourhood friends. Start slow and gradually build yourself up to do 45 min-1hr every day.
The combination of diet restriction and exercise is sure to make you lose weight. When you do not have to carry around so much weight, you start feeling better and more energetic.