You might have a urinary tract infection. Do you have any issues with diabetes or high blood pressure? Sometimes protein gets in the urine when you have either of these.
Most likely it has something to do with ketosis and / or low carb diet. Have you talked to your doc at all about it? Maybe you need to drink more water, as well. Urine should be diluted, not overly yellow.
That's all I have about pee! And I am surprised I had THAT much!