Have you tried celery with your tuna/mayo? I don’t like celery except with tuna/mayo: crunchy and delicious, especially between two slices of whole wheat bread on which you melted some cheese….yummy! You can eat half of that sandwich at lunch and the other half 3 hours later, between lunch and dinner.
You should eat some fruits (I know tomato is a fruit, but I’m thinking…an apple or a banana sometimes).
You should not go more than 10 days on a low calorie diet or you might risk the chance that your body will have time to adapt to low calorie requirement, lowering your metabolism to reach that goal and making it extremely difficult for you to use your fat reserves.
Then, you’ll stop losing weight and as soon as you start eating normally again, you will make fat reserves very easily.
Losing weight by eating a low calorie diet is never really a lasting solution. In the long run, it usually even adds to the problem by messing up your metabolism. You should eat as much as your Basal Metabolic Rate, which is about the level your body will not adapt and lower your metabolism. Then you should exercise for 3,500 calories for every pound of fat reserves that you need to lose.
That way, the more you exercise, the more muscle mass you get. The more muscle mass your get, the stronger you become, making your workouts easier and more efficient and making your metabolism higher…so you can eat more without gaining weight (each pound of muscle mass needs 50 calories a day, just for maintenance, not even counting the exercising).
I wish you the best.
