Late period?

Hello! So I experienced all the usual pms symptoms, cramping, tender breasts, sore nipples, a little fatigue, etc, but my period is 2 days late. I've never had a late period in my life except when I took plan B a year ago. So I run out to the dollar store and get a cheap pregnancy test until my paycheck hits tomorrow and it was negative? I'm confused now. I'm still experiencing cramping and very tender breasts and slight nausea, why was it negative? Should i wait longer or see a doctor? Thank you!