Positive hpt, negative blood test, brown period for 4 days and this month brown discharge for 1 day, what can cause brown periods and spotting?

Old blood: Brown blood is simply old, so it's coming from a source that is bleeding very lightly and very slowly. Regular periods can start and end with a little brown blood but are typically bright/dark red due to the speed at which the uterus sheds the endometrium that gets regenerated monthly. A negative blood test is definitive, so your HPT was a false+ Get pelvic ultrasound & Pap to eval uterus & cervix

Miscarriage?: May be you had a false HPT. Or you are having a miscarriage. You should get examined.