Late period. URGENT ADVICE PLEASE!

My period is six days late. eve had already notified me that this period is going to start on a different day and that different day was six days ago.... I wasn't having any signs of a period either. No cramps, my breasts weren't tender, I wasn't being pissy. But I was craving sweets for a week 1/2 straight. I'm starting to get some lower back pain which is normal of me when I'm about to start and I have been constipated. I took a pregnancy test four days ago and it came out negative. Any advice? Should I take another test?