Your problem is that you are still consuming more calories than you are using. This problem can be complicated by the disease processes you are dealing with, as well as the medications you have to take. It will just make weight loss a bit more challenging for you.
In order to lose weight you need to use more calories every day than you eat. And since, obviously, you are still gaining weight at 1500 calories this mean a couple of things.
1) you need to eat fewer calories
2) you need to boost your metabolism so that you are using more calories than you currently use.
A few suggestions:
---Make sure there are no "hidden" calories in the things you eat. It is very tempting to look past the little amounts of sugars in salad dressing, ketchup, etc. Also, favorite food seasoning and cooking utilize fats which can also be easily overlooked.
Eating out is a problem. The restaurant may "say" its a low cal salad, but unless there is nothing on it---its not low cal. Just examples.
---Watch portion sizes, even weighing foods if you have to until you are accustomed to what a portion size is.
---Eat the right balance of different food groups during the day. Another dieting mistake can be counting only calories, and paying attention to the variety of food it takes for good nutrition.
---Get active. Losing weight successfully takes a balance of diet and exercise. Your body needs to move and exercise its muscles for good health and proper utilization of the food you eat.
Here are a link to the Food and Fitness section of the American Diabetic Association. Under the "Food" section is another section called "create my plate" with advice on types of food you should be eating, how much and when. Use this as a template for types of foods, while still counting your calories. You may have to reduce your calories even further, but do not go below 1200 calories.
Also, the links under "Fitness" have good suggestions on how to get moving. More activity leads to feeling better, which leads to more activity and if you keep it up, you will be able to eat more and still lose weight (or maintain once you reach your goals).
All of this, of course, needs to be discussed with your physician. And I am assuming you are watching your blood sugar levels as well. For a diabetic, medication and dieting can be a delicate balancing act. That's why more activity is so essential.