I HAD THE SAME THING IN JUNIOR HIGH!!!! Cept mines was about an inch bigger.. mine was HUGE! And it took like 2 weeks to heal... I think its a spider bite because when it was almost healed.. you could see bites of twos.. like 6-7 in pairs all around.. (you can only see it when its almost completely healed).. i dont know what kind of medicine/cream to use.. my mom just used whatever we had and smeared it all over my arm everyday
poor girl... hope it heals faster than mine did!