Mazal tov on the recent birth of your baby!
Unfortunately it is impossible at this point to tell if this bleeding is caused by the minipill, or if it is simply a resumption of menstruation. Many women who fully breastfeed still menstruate regularly (or irregularly). Each woman and each birth is different, so even if with previous births you nursed clean, or if you heard from friends about their experiences nursing clean, it is still normal and common for women to menstruate while breastfeeding.
On the other hand, it certainly is possible that this bleeding is caused by the minipill. Especially during the first three months (and unfortunately for some women, even after) irregular bleeding/spotting is common. Taking the pill religiously at the same hour each day may reduce the chance of staining. It could be a matter of giving the pill some more time and seeing how your body adjusts; on the other hand you may continue experiencing irregular bleeding for the duration of the pill. It is impossible to know in advance whether you will continue bleeding from menstruation even if you stop taking the minipill.
It is important to note that not all bleeding will render a woman niddah. If you are not experiencing an actual flow of blood (comparable to a period), rather staining (even heavy staining) you may take precautions against becoming niddah from the staining. See our article on stains for more details.
If this bleeding is causing you significant distress, you may wish to discuss with your doctor switching to a regular combined birth control pill (and possibly extending your cycle to minimize your time as niddah). While it is not the preferred method of birth control while breastfeeding, it is safe for you and the baby. However, it may decrease your milk production. If your milk supply is well established, you can start taking the combined pill while taking care to increase both the frequency and length of feedings to compensate for any decrease in supply. Alternatively, you can wait another few months until you start supplementing your baby's diet with solid foods before starting the combined pill, and then any decrease can be complemented by solids.
As a final note, it is possible that your feelings towards niddah are caused in part by postpartum depression, which is quite common. If you are having difficulty coping in other areas, or if you are frequently feeling down or depressed, please don't hesitate to reach out to your doctor, or other organizations that help women suffering from post-partum depression such as Nitza or Sparks Center.
Please feel free to get back to us with any further questions.
B'Hatzlacha!