Hi, I missed my period on due on the 12th of nov I had sex on the 10th of nov after being a week late I took an hpt which came back negative, I then had sex on the 20th of nov, today is the 29th of nov and I had some light brown discharge this morning, what is this ?

You should probably take a HPT now. The best time to test is two or more weeks after your missed period, before then the chance of a false negative are pretty high.

Light brown discharge is usually old blood being sloughed off from the uterus. It could be the start of a full blown period but it could just be random discharge. Assuming it isn't accompanied with pain it, in upon itself, isn't something to be too terribly concerned about. Though the missed period would be.

Test again, and if that goes negative then make an appoint with your OBGYN to have a, "Okay what is up with my period and stuff" session.