Hi there
I dont know anything about charting etc...however, I was really confused as I got my period when I would have been pregnant as I found out I was 8 weeks, when I had my period 6 weeks earlier....It was (appeared as) a regular period so was really confused too...so maybe you are?

I would do a HPT to be sure...*fingers crossed* I do hope you aren't m/c-ing though

good luck