Don't know when i ovulated, but can implantation bleeding happen before a missed period?

Yes: If bleeding happens with implantation of the fertilized egg, it will happen within a few days of conception. This will be before you miss your period.

Implantation bleed: Yes implantation bleeding can occur before a missed period

Yes: If you become pregnant, this happens about 14 days before your period. Implantation happens just a couple of days after fertilization of the egg by sperm, thus it could be a full week before your period that implantation occurs. If you have implantation bleeding - although it really doesn't happen very often actually- it would occur days to a week before your period is late.