Thanks for the query.
Since you are on birth control pill, less likely you are pregnant.
However its always better to rule out pregnancy
as your symptom of spotting could be an implantation
bleeding. I suggest you to get a HPT done and an ultrasound
to be more sure.
If pregnancy is ruled out, there is nothing to worry.
Its a side effect of birth control pill called breakthrough bleeding
. You need to continue taking the same.
If same symptoms continue for more than 3 months, its recommended to increase the dose of estrogen.
Hope this helps,