period post-appendectomy

Sydney
I just got my appendix removed Wednesday morning! I'm not supposed to start my period for another 12 days but it suddenly started this morning? I'm not having any pain but I'm not sure what to think of it starting so early, does this have anything to do with the surgery? (Also I am on birth control but didn't start taking it again until Friday) could this have thrown off my hormones to cause this?