What Causes Spotting Before Periods?

Hi, i have brown discharge a week earlier before my period is due. I've been in this condition since several month before, 3 times specifically. But not continuous. one month early brown discharge, then the next month is normal. Right now its already been 6 days, and i'm kind of concern a bit. Trying to conceive since early this year. Pregnacy test always negative. Easily stressed. Been pregnant last year but miscarriage at 3 month due to too much stress. No pain with brown discharge. Is this normal? or does it got to do with my hormon level?

Age: 30

Height : 155 cm

Weight : 43 kg

Thanks