Hello. Let me tell you from my own experience (and I should know, cos I've been overweight/obese since I was 4 years old) that the strict diet you're on will indeed make you lose weight pretty fast. That's the good news. The bad news is that weight which you lose fast comes back with the vengeance just as fast! I've had times in the past where by simply not eating anything for almost a week I could lose 5-6 kilos... and it would take me a week or two to put them back on with reinforcements! In order to achieve something durable, you must not starve yourself. You can occasionally have 1 day with zero or close-to-zero calories, but that should only be occasional. The secret is to lose weight slowly over a longer period of time. If you lose like 4-5 kilos per month, that's a good rate. Second, I dunno if you're a vegetarian or not, but it's a healthy idea to eat some meat as well, your body needs the proteins. It's a good idea to have for example 200 grams of meat and some raw vegetables for lunch. This "trick" was my main battle plan, and it lost me 22 kilos (that means almost 50 pounds). Good luck and remember, don't starve yourself, it's not healthy

Oh, and another thing, many doctors actually recomend that you quit coffee alltogether while you diet. Especially since coffee is not good on an empty stomach, and considering that you only have watermelon, that thing is 90% water so your stomach will be empty

Cheers