Is it possible to have a period then implantation bleeding because I had my period on april 16-19 an today the 21 I'm having light pink bleeding?

Take a test. If you had a normal period, then it is unlikely that you are pregnant this cycle. However, it may be difficult to tell whether your bleeding is from a period or is implantation bleeding. Take a pregnancy test and if positive, make an OB appt. If it is negative, you may consider repeating it in one week to be sure.