Hello,
Thanks for the query,
Blister in mouth after sexual intercourse points towards
herpes.
Brownish discharge can also be seen in herpes,
Though uncommon.
You can get a smear done from the blister.
This will help in diagnosing herpes.
Please meet a
dermatologist for final diagnosis and treatment
Let me know if you have any other doubt.
you can ask a direct question to me on this forum, following the below link.
http://www.healthcaremagic.com/doctors/dr-rahul-kumar/64818
Wishing you a good health.
Thank you