What Causes Headache, Loss Of Appetite And Weight Loss?

Hi, I am a 15 year old female and I have been getting bad headachs and i have lost my appitie and lost weight. I am not sure what is going on. i have talked to my doctor and she said theat the headachs were just because I had a cold, but I got rid of the cold about 3 or 4 weeks ago and I still get the headachs quite frequently.