no period!

Hi, so I take the pill regularly, I'm pretty good at taking it every night I rarely forget, but on Saturday I started my week break and I've still not got my period. I've had lots of brown old blood during the pill break and the week before but not my period. I've taken a pregnancy test and it was negative and I've had the normal hormones I get during the week break but I'm getting a bit concerned! Has this happened to anyone??