Is it possible for implantation to start just after onset of period and cause a short period + successful implantation?

Not if you're a guy: Assuming you are asking for a female. This is unlikely but possible. Maybe there was a successful implantation, that led to a little bit of bleeding, that was felt to be a short period? Wait 2 weeks and check a pregnancy test. That will give you a more definitive answer. Waiting sucks though, I know. You could check a pregnancy test now since two tests usually come in the box.