The subchorionic collection is small. Most probably subchorionic bleed is coming out. Brownish discharge can be that subchorionic collection blood and it may be coming out which is dark red in colour. Continue progesterone supplements advised by your obstetrician.
Do visit your obstetrician if you develop any fresh heavy bleeding associated with clots , crampy pain in lower abdomen.
If you want to discuss more, you may have a video consultation by booking the slot.