Please help! What's happening to me? Cramping and spotting at 12 weeks when trying to wean off progesterone

Not the progesterone. The shift from maternal to fetal (placental) Progesterone production occurs much earlier than 12 weeks. In ivf cycles the data would suggest that stopping the p at 4-6 weeks is safe but most dr's wait until 8 weeks to be safe. The symptoms are most likely coincidental. If it makes you feel better and ok with your dr, probably ok to continue for some time.