I am trying to lose weight. Heard that after a few days you don't feel hungry. Is that ketones?

Not true. Regardless of what you eat, you will always feel some hunger you just won't be famished if you eat the right foods at the right time. Losing weight is a complicated process and requires effort and dedication particularly if you have been overweight for a long time. Get some support and knowledgeable advice. Speak to your physician.