Are Super Mutants created? Because i remember something about mutants being created in Fallout 1, by a doctor or something. And where do they reproduce in Fallout 3?

They were created by infecting people with the Forced Evolutionary Virus (FEV). They are all sterile, so the only way for them to reproduce is to capture more humans and infect them as well. See:

http://fallout.wikia.com/wiki/Super_mutant