Question about teeth, and insecurity?

I am very insecure about my teeth! They are straight, but when i was little i fell with a play block in my mouth and it knocked one of my baby teeth loose, and it turned grey, but it fell out, and now when my two top front teeth grew in they had yellow stains on them, BIG yellow stains, and i brush my teeth everyday with the arm and hammer whitening tooth paste and they NEVER get whiter. So im really insecure about it, im 14, and i almost like cry when people are like 'oh your teeth are messed up' or 'do you ever brush your teeth?' and lastly, they say 'umm, you have something on your teeth'. Its really embaressing, and i hate it! And i dont have alot of money to go to the dentist every few months to get them whitened.. I dont even know why i have the stains"/ pleaseee help me...