Ladies that have taken birth control pills advise.

Ladies I am so confused. What are the most common side effects of birth control. I am on my third week of taking a low dose birth control, I missed one day but then took it next day like i was supposed to. So then after a day or two I started spotting brown discharge, then it turn pink then brown blood and im still spotting its been 4 days. To makes matters worst my boobs hurt like crazy, and im cramping a little bit. Can this be side effects or possibly early pregnancy symptoms. My period is due on 10/25 which i think too soon for pg symptoms. Or have you guys had this and turn out pregnant. Please share your stories 😊