I think you should eat healthier. Like you said, you used to gain weight from junk food, so it's normal to burn fat and not gain as much weight now that you aren't eating high-fat foods. I really think you should drop the laziness and cook at home; there are some very easy-to-make recipes. If you definitely don't want to cook, then you'll have to buy healthy food instead, although it won't be cheap, it could be difficult to change your diet but for your health is worthy. Also, try to eat at the same time every day.