What Causes Red Bumps On Hands, Legs?

hiiii, so i have scars on my arm kind of look like a line, theyre from scratching. they're about a month old, and they have several red bumps in them... and on my handi have just red bumps... no scars. same with on both my feet, and in random places , what are they possibly from? I'm only 15 so i dont think its an old lady thing hahaha.