I have recently noticed that it takes 3 months or more for my bruising to go away and wanted to know if i should be concerned about that?

YES: It does depend on whet areas are bruised and size and kind of tissue involved. At your age 3 months is uncommonly long. See your md and you may be referred to a vascular md for evaluation. Could be bloodwork turns up something, capillary fragility, diabetes, any number of syndromes. See the md soon. The external bruising is what you see-- you may have internal as well.