HELPP!!!

Ok so I'm due to start my inactive pills on Sunday(I've been on BC for almost a year.. and no I haven't missed pills) I started having brown discharge yesterday but it seemed to go away and was normal again. Well I just went to the bathroom and I have started my period?? I'm not due to start until next week. Does anyone know what could cause my period to start early on birth control pills? I'm kinda freaking out...

** random info- I'm a virgin and I had my gallbladder out a month ago..