period or implantation signs

I'm probably just overreacting but the first week of this month, my boyfriend and I had protected sex. We always do. We have ever since we started dating. Usually we have sexy several times a day since we are in a long distance relationship and can't do it every day. 
My period was supposed to come today. But the past few days, I've been crying over the weirdest things and getting really angry over everything which are common PMS symptoms and all that. But I've also been getting nauseous and dizzy and have back pain. Normally I don't experience any of those during my period or before except for back pain occasionally and anger at random things. But I've also been really bloated and. Reading out in acne (also two normal signs). But today, I noticed that on my pad was almost like brown discharge. Usually my period starts right away and turns from brown to red and I get little manageable cramps. This time though, all I've had is the brown discharge like stuff and very little blood. No cramps either. Is it possible it could still be my period but acting differently or is it a sign of implantation?