BROWN 3 DAY DISCHARGE PERIOD NEG TEST?

ok I'm very confused and would appreciate some help! My period came this month accept it was not really a period, it was like brown discharge with the occasional red spec, I used like a tampon per day and it barely srained them (without sounding graphic) and lasted from weds 22nd to fri 24th (yesterday). i was around 3 days early. I have also had sore nipples and lower light cramps. I tested this morning with a tesco test and it came back with a reeeeallly faint positive line. I then tested on clear blue digital and it said 'not pregnant'? I have an inkling that I am but want to know people's thoughts?