brown vaginal bleeding after sex

my girlfriend is continously having this mild brown vaginal bleeding for over 2 and a half weeks now,
enough to fill a panty-liner per day (not like her normal period)...
sometimes it was accompanied by small brown blood clots...

the bleeding occured a day after we had protected sex...
she's under a lot of stress(family matters)...

she has normal cycle (between 30-32 days) and lasts for 5-6 days...
today, her normal period is a week delayed...

were worried that she might be pregnant and experiencing implantation bleeding but from what we've heard,
implantation bleeding occurs for a day or 2 only and has a pinkish-red color...

is it really implantation bleeding???
if not, what may cause this???
and what treatment should we try to stop her bleeding???
my girlfriend is not into the idea of visiting an OB cause her parents may get angry if they knew about this....

please share us some insight about what maybe happening...

thanks everyone...

and thanks to ms. susan for some insight earlier but we would like to get
a 2nd opinion about this matter...