Implantion bleeding or PMS

So I've had a pregnancy scare and yes it's very scary, but my period started today the day it was supposed to start but it's spotting light spotting with brown spotting with it. Not to mention that I have bad cramps too ..... It might just be my PMS symptoms.... Like nausea from cramps, fatigue, tender breast, back pain, very emotional, bloating etc... But I want to be in the clear, for sure. I took a test before but it said negative but I still have the symptoms of PMS like almost a month before my period which isn't normal. I know my body and I've never experienced this so I'm getting paranoid and stressed out about it ... Any suggestions.... Am I just making it a big deal and it's nothing serious or should I be concerned? Thanks