period 4 days late now spotting

Anon
Sorry if this is a dumb question guys. My period was due on Thursday and it's now Sunday night and haven't gotten it. I had a tiny bit of light brown spotting yesterday and this morning but now nothing. Do I count that as my period? Seems a bit late for implantation bleeding. So I figured I'd take a test, I used my second pee because when I first woke up I forgot, it came back veryyyyy negative. (I also spilled the cup of pee all over my bathroom floor, but I digress) My breasts are only very slightly sore and had a really bad cramp Saturday morning. Other than that I feel normal! What the hell is going on. 
Side note: I'm a healthy 21 year old and I'm always extremely regular