Haven't eaten in almost 4 days?

my dr put me on some new medicine to try out cuz he thinks i have ADHD and it makes me not wanna eat everytime i try to eat it makes me sick. i ate some sour skittles a milkshake and a banana within the last 4 days. i can't eat and i can't sleep. All i have been drinking is water and maybe a coffee in the morning i have lost 5 pounds since tuesday and i can't sleep at night. I got 3 hours of sleep tuesday night. and then Wednesday i couldn't fall asleep again until prolly 1:30 - 2:00 am. im not sure what to do about it. Im very angry and mean when im co-ming off the pill. i don't know what to do. i noticed that it does help me concentrate more in school and it's helping out which is one of the main reasons i got it. any suggerstions