I have gone through your query and understood the concern. The cause of this bleeding is most likely due to the hormone imbalance
created by the tumor
, precipitated since you have stopped the medication. The physical appearance of the bleed suggests a breakthrough bleed, as it is of brownish color. The presence of fibroids, especially if they are significantly large and located beneath the endometrial layer or in the muscular layer, can accentuate the effect. I would ask you to get further help from a specialist through proper clinical evaluation. Take care.