I suddenly lost my appetite ..?!

Well , i went to the doctors a couple days ago , and since that morning , i have lost my appetite . Like i went to the medical lab so they can do a bunch of tests on me , took make sure on my blood and stuff , and my heart . so i have to wait about a week to find out if im in good health or if somethings wrong . So that afternoon after the medical lab , me and my dad went to a restaurent cause we were both starving , and i couldnt eat from 7:00pm last night, because of the tests . So at the restaurent , i was so hungry , and once my food ordered , i only took like 3 bites , and i didnt feel like eating anymore . BUT i was still hungry . thats what happened last night a dinner as well . And now im even more concerned because i was doing research yesturday, and found out that this can maybe be a sign of cancer . SO I AM REALLY SCARED . i am 13 , turning 14 in a couple months . i usualy eat normaly too . I am 5'5 (1meter and 66 inches) and weigh about 44,4 kg , or about 100 on the scale thing .
Please help .
Thank you very much everyone =D
Jonathan