It looks like you have had a breakthrough bleed. This can happen if the dose of hormones received through your pill is not enough; this may happen due to weight gain, emotional disturbances, stress
or haemopoietic disturbances. Please see your health care provider for a local as well as a general exam as you need to exclude local lesions like a cervical erosion or infections and vascular complications secondary to the pill use. Wish you good health.