Had Protected Sex. Missed Periods. Pregnancy Test Negative. Discharging White With Brown Stains. Reason?

So my last couple of periods have been irregular (20/09 - 28/09, 15/10 - 21/10, 15/11 - 19/11, 05/12 - 10/12) but this month, it came on the 20th of January, and is still going. During December after my period, I have safe sexual intercourse using a condom and my partner said he pre-cumed when he was still in me. When he took it out, I checked that the condom was not broken so it was all clear and safe. However, I was expecting my period to come around the 5th - 10th of January but It didn t so I took a pregnancy test and it was a negative. Since the 20th of January, I ve gotten brown blood instead of red. It has happened before, long before I had lost my virginity also so I m confused as whether it is spotting, my period or something else. It s been 8-9 days and I still have this. It s very very light, and very dark brown. I don t have any cramps whatsoever. Just then when I wiped, I found out that there was white discharge on the tissue but light brown stains around it, technically not a brown discharge. What do you think? When should I take another pregnancy test?