This is totally normal just before your period is due. Brown blood is old blood, and so this is just your body flushing out whatever is left in there from a previous period just as the new one is starting. Sometimes, it can be a sign of pregnancy - but since you tested and it was negative then makes it more unlikely. Unless, what you had what maybe some sort of implantation bleeding, then it would be too early to show on a test.
Wait a week. If your period starts, then you know you're not pregnant, it and it was just pre menstrual bleeding. If a period doesn't show, then take another HPT with first morning urine.