Today I got some blood in my underwear, and yesterday and today were my expected days of my period.
The spot of blood was more than a few drops, it was a spot about an inch long, and it did soak through my underwear so I could see it on the other side of the fabric.
But when I checked my pad later today, I noticed that the blood looked almost brown and didn't look like normal period blood.

Any thoughts on what this could be? My boyfriend and I had sex on the 28th of January without a condom, and he never came in me, so I see it as unlikely.

I just need to know if this sounds like a slow start to my period, or a soaking-through-my-underwear spotting.