Thank you for reaching out to us.
Bleeding from a vaginal cyst does
not render you niddah because the source of the blood is not the uterus. Since the bleeding occurred immediately after touching the cyst, and your doctor believes that this caused the bleeding, that is sufficient to attribute the bleeding to the cyst. You don’t need to be further examined by a doctor. As you say, it is also not likely to be your period since you are only a few months after giving birth and fully breastfeeding, which is further evidence that the bleeding was likely caused by the cyst.
Please feel free to write back with any further questions. Refuah Shleimah!