Help!! problems with eating and drinking!?

I was a growing girl so I used to eat all the time and still stay skinny. well for the past few months I haven't been eating as well as I used to and sometimes not at all. my stomach used to grow all the time and really loudly and it could really hurt! but at some point my stomach stopped growling, stopped telling me it was hungry, and stuff like that. I can't eat as much as I used too. I get full to easily and at least feel like I'm full. like right now I didn't eat dinner and all I ate today was a small chunk of water melon, a few Hershey kisses, and at least one cup of milk. and today I did a lot of yard work and heavy lifting all day, normally my stomach would be growling a lot right now. I'm scared that I did something that could have messed up how my body works. after a few months of this I started to get super shaky I couldn't talk sometimes and I would be exhausted! to tired to move and think. then I realized that I haven't been drinking enough water lately, sometimes I would barely have a couple sips a day, and sometimes I would go about 2 days without water (and I think if you don't drink water for 3 days u die). I've tried to get back to the way I was before but I'm having trouble I can't eat as much as I use to and it seems like I mentally and physically can't do stuff. my grades are slipping to and normally get straight A's. I do a lot of physical activities and stuff. I didn't try out for track this year cuz I was scream that if I didn't eat enough that I would start to get sick and possibly p out on the track. I'm really scared and I really need help, I want to be skinny but I dont want to have to deal with all of this. I want to go back to the normal girl I used go be not this 14 year old who cant eat, think, or stay awake. PLEASE HELP!!! I'm scared out of my mind!!