"i have been on phentermine for 3 days. i have lost 7 pounds. highly due to the fact that i haven&#039;t eaten much of anything. i have walked everyday for 30 min a day. i take the pill when i wake. i have had a headache everyday about 3 or 4pm. i believe its because i am not taking in enough calories. i am also taking birth control and a women&#039;s multivitamin."