is this implantation, or af?

Alexia
i am 4 days from when af is due and today around noon I started bleeding. it's rust red, and not a lot, not gushing, but more than spotting. I've had cramps all afternoon. they aren't bad. my usual cramps are unbearable to the point of locking myself in a dark room. now they seem to have tapered off. af is never ever ever early, if anything a couple days late. 
​I took a hpt today and it was negative. I'm going crazy!! could this be implantation?