Hello
Thanks for writing to us with your health concern.
Having sex on while on your periods carries almost zero chance of being pregnant.
Only anecdotal reports are there.
As your period has stopped, do not worry.
If you normally have a brown discharge, it is not unusual in any way.
If the brownish discharge is for the first time, then it could indicate 
stress, weight gain, late nights etc.
If the spotting persists or recurs, please see a gynecologist to rule out 
thyroid hormone imbalances, 
polycystic ovarian syndrome, 
endometrial hyperplasia etc.
If you wish to avoid 
pregnancy and risk of STDs, best to use condoms regularly.
As your ovulation is still many days away, I think the possibility of your getting pregnant is next to none.
All the best.
Take care.