Make sure your protein intake is high enough or you could be losing muscle. 2 eggs is only about 12g of protein. Maintenance levels of protein for a very physically active person are at least 1g of protein per lb of body weight (~2g per kg). Take this with a grain of salt, as it is subjective -- depending on your current physique, you may wish to lose muscle (for example: if you are a pro bodybuilder and wish to become a triathlete, significant muscle loss would be desirable).
You may also want to pick up some skin fold calipers to monitor your body fat. Your loss of weight should not be coming from lean body mass. Body fat percentage will be a much more helpful piece of information than BMI.
Ultimately (and most importantly) are you seeing quantifiable improvements? The essence of all training is progressive overload. The matter becomes: are you bettering your lap times? If so, continue until this begins to plateau, then start examining your diet more thoroughly.
One side note: feeling tired enough to sleep 2 hours after your swimming sessions seems to suggest to me that your carb intake may be a little low. You may want to add some sugary electrolytes (sports drink) to your diet around the time of your workout to keep your glycogen and electrolyte levels up.