Brown Sticky Discharge Before Periods

Every 3 out of 5 months, a few days before my normal blood flow, I get a flow of this brownish, sometimes reddish brown, sticky goop, and I can't figure out why. I've red a few medical journals and it says that brown discharge can mean A LOT of different things, its starting to make me nervous. Does anyone else get this, or tknow what it might be? Is it part of my period, or spotting, or what?