I have a mark on my arm from sucking on it as a small child. it looks like a hickey basically. what would happen if i tattooed over this mark?

Doubt it: If you have a mark there, I doubt it has anything to do with your teething/sucking habits as a baby.Those all heal if the skin is normal.You likely have congenital skin defect or nevus.These often have irregular depth and a collection of blood vessels underneath. If you know an experienced tattoo artist they can look at the skin and let you know how well a tattoo would take/cover it.