There is quite chance of being pregnant in case of unprotected sex around ovulation time. Therefore, I suggest you to undergo a blood test
for beta hcg & one TVS scan to confirm product of conception as late period with brown vaginal discharge
is mostly suggestive of implantation
In exclusion of pregnancy
, you may need to do some investigations to rule out other pathology like thyroid profile & other hormone assay etc. Consult with your doctor and take suggestive measures.
Avoid stress / anxiety, take healthy diet with folic acid
& vitamin supplements, take adequate bed rest and maintain genital hygiene properly.
If you need further consultation with me, then you can visit http://www.healthcaremagic.com/doctors/dr-soumen-patra/63326.
Take care yourself.