late period, brown discharge

Hey ladies! my period was supposed to start on Dec. 8th, I'm now 20 days late.(My periods are no more than a day or 2 late) I'm now experiencing a light brownish discharge with very mild cramps. (As of a few hours ago) We have been TTC for what seems like forever!! I've taken 2 hpt that both came back negative. (The last one taken like 3 days ago) My question is, do y'all think it could be AF coming around, or just early pregnancy discharge? My boobs have been really sore lately and I've also had slight nausea in the mornings and during the night.