Have started having a brown discharge after day 5 blastocyst now day 8 pt

Implantation bleeding can occur anywhere from 48 hours after transfer and as late as 5 days after. Not all women have implantation bleeding, I think the statistic is like 25% of women have implantation bleeding.

You might be experiencing late implantation and therefore have the brown discharge or worst case scenario...you're getting your period.