Why do I worry about being pregnant so much??!!!?

Why do I keep worrying about getting pregnant?

Ok, I’m 12, and a virgin. I had no sexual contact with guys whatsoever. I do masturbate sometimes, and that is sometimes. I do try to stop cuz’ it’s a sin, and seems gross. Anywayz I’m really scared about getting pregnant. Idk why though. I had my period just this year in February. And, I stopped masturbating ever since then. But, then one day I did it again, got extremely scarred, and quit eating. Then a month later *right now* I started eating normally, and maybe a bit more. But, I’m really scared because I have all the signs of pregnancy, and I’m really scared!! I’m irregular and my periods only came four times this year and they were all REALLY LIGHT, brown, and only lasted 1 to 2 days. I had my fourth one maybe a week ago, but I’m still scared. It’s been a month since I masturbated since my period and it seems like my stomach is getting bigger. Right now I’m 5,3 ½ and I weigh 110 pounds. I’m just really scared, and I starved my self all day today and I have really painful cramps. What do I do? I’ve only drank water and chewed gum all day…--_-- I’m really scared, plz answer this