Early period and ends early

Two weeks ago I had unprotected sex with no pill, nothing. After I sucked him there wasn't any precum left, so we did like 5 strokes and stopped. Later we just played around and I kept rubbing my pussy on his dick but not his tip. That's pretty much it. Now I'm supposed to have my period next week on the 18th yet yesterday I got terrible cramps during work. I went to the bathroom and bled a little, and then all of a sudden it stopped. Then I woke up for the next morning and I did not bleed last night when I checked my pad. It is now 4pm, and I check my pad and from the looks of it it's a little ball of discharge and is brown and has a little brown stains, kind of looking like blood that's been out for a while. What's going on? Is it just a slow period coming? Or... what😭 please help me!