late period

I usually get my period right on time but I am now 3 days late. I spotted a little Thursday (very little) and then I though I started Friday because it looked like my period but I guess it was just heavy spotting because I haven't had anything else so I took a test today and it said negative. I am also cramping a lot more than usual. I usually cramp right before and at the end but it's very mild and my nipple are sore and sensitive and that's not normal at all. I'm not sure if I should keep waiting for AF to show or see about a blood test.