Instant loss of appetite?

Two days ago I was eating fine (probably even over eating a little bit) but after that I just didn't feel hungry anymore so i didn't eat the next day. i barely had anything to eat that day and i noticed that my stomach hurt a lot because of hunger so i ate a bowl of cornflakes and a green apple as a snack around 7pm. Today I woe up many times because I was so hungry then at around 10pm had some toast and scrambled eggs then quickly felt better and pretty full, throughout the day i nibbled on some things but wasn't able to eat much at a time, now I didn't want to eat anything because i felt full (i felt a little depressed and mentally exhausted after a long fight with my sister) I had a can of coke instead. when i finished drinking i felt really hungry and weak. But right now i'm forcing myself to eat an apple because my stomach hurts so much that i feel sick after taking the first bite. I'm scared that i'm going into depression or anorexia. is there anyway to keep myself from slipping into anorexia? Am i sick?