Birth control does have a common side effect of vaginal bleeding at times, but in a scenario similar to yours it is best to rule out pregnancy
and thos should be done at least 2 weeks from the suspected date of conception or on or after the first day of a missed period using an early morning urine sample. It would be wise to rrpeat this test 2-3 times with a days gap between each test.
Once pregnancy is ruled out we can assume either contraception
or infections to be the cause and will have to be further evaluated by a doctor.
Hope this helps.