TTC, very late period neg hpt, brown period?

hi there, this is my first time writing into one of these forums, but i need advice badly. My last period was on 18th june 2012 and im usually 28 day cycle so due again this month on or around 16th july. I have taken quite a few hpt and got BFN :( even one AT the docs was neg too. today i have had some brownish blood only when i wipe after going to toilet, not sure if this is AF rearing her ugly head or something else. I am usually quite heavy with using both tampon and pad, (TMI SORRY) my DH and I have been trying to conceive for almost a year so got our hopes up with being late to be disappointed with BFN. i have been sick a couple times, have headaches every other day and got some serious heartburn the last few weeks, i havent been cramping (at all) like i usually do when AF is coming to visit. i am also VERY MOODY (poor hubby). Could i still be pregnant or am i hoping too much?? any advice is greatly appreciated thanks