weird spotting instead of period?!

M
I was due for my period on the 12th, when I wiped it was super light pink. So I put on a pad.  Barely anything all day. The next day I put on a panty Liner and there was barely anything but a small amount of brown discharge. Today there is absolutely nothing. I had protected sex on the 6th. I've never had any spotting like this before and I usually get a heavy crampy period each month. I would take a preg test but I don't want to waste my money on taking it too early. 
Just posting to see if any of you girls have had anything like it?