Hello,
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You had bleeding after sex once. I assume that you otherwise in good health. In that case you need not worry about this single episode of bleeding.
But if this bleeding recurs you will need to get tested for STDs especially for a fungal infection like yeast infection, as these can cause bleeding after sex. If you have any other symptoms like pain while having sex, pain or discharge from vagina, painful urination etc please let me know.
In that absence of the above symptoms the uterine bleeding could be due to a fragile uterine epithelium, which is a concern only if it repeats.
Hope this helps
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Thank you