I've got a question for everyone, I'm 13 days late getting my period a…

I've got a question for everyone, I'm 13 days late getting my period and I took a home pregnancy test and got blood down and they all day negative, so I'm not sure what's going on. I've been on my birth control for two months now, I don't know what's still wrong, I haven't gotten it yet. My last period was March 15th and we are almost done with the month of April and I still haven't gotten it. Need help.