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It may be decomposed decidua that is the shed internal layer of uterus
which is a normal phenomenon but the white thing on it may be due to candida also.
Candida is a fungus and may cause infections at times.
You should get a gram stain and culture/sensitivity of the discharge and if needed take antimicrobial therapy in consultation with a gynecologist.
I hope the advise would be informative and useful for you.