If you haven't been a daily weigher before you might not be aware it's not uncommon to fluctuate weight of up to 2 kg per day...depending on time of month (which I gather may have stopped now for you) salt retention, fluid loss etc. A total of 6 kg is a lot to lose in 4 weeks unless you have dramatically changed your diet. So think about...
-Have you cut out lots of processed foods?
-Have you stopped drinking sweetened soft drink?
-Have you suddenly stopped alcohol?
-Has your appetite decreased or are you nauseated?
If it's no to any of these things then you might need to discuss it with a GP or your prescribing Dr...sooner rather than later just to ensure no issues.
Kath x