hormonal changes, insertion of objects, stress, undiagnosed vaginal infection, implantational bleeding (one of the first signs of pregnancy), among others are the main causes for bleeding between...
birth control manipulates your hormones to prevent pregnancy....your body is trying to normalize. you may need a higher dose pill. check with GYN doctor
Period blood can be dark brown, light brown, dark red or red. Sometimes your period is brown if it is a light period. Sometimes your period can be brown near the end of your period.