You need to have an exact daily amount of calorie intake, take a certain number of calories per day, not more or less than that, for example 1700 calories. That's just an example and you should figure out you BMR so you know the exact number of calories that you intake. Keep your diet clean.
Also, measuring weight is a wrong way of determining if you have made progress. You should determine your progress by measuring your body fat percentage, you can buy a device that does that or simply tell your doctor to measure your body fat level.
The human body is mostly water so you can easily manipulate weight.Many popular and not-so-popular athletes intentionally dehydrate their body and loose about 3,4 kilos in one day, in order to get to a lighter weight class. Of course after they restart the normal hydration process of the body they regain the weight instantenously. So don't get too upset if you gain a kilo or two, get upset if you gain 5,6 kilos or more.
I'd recommend you to excersize at least 3 days per week and do cardio also,1 day per week is too little. Swimming is a good cardio, and for better results you may also apply HITT on that. And of course the most important thing is the DIET