I'm late

Tina

So Wednesday I had worked all day and once I got off I was so happy to sit down ( I stand for my job) my back was hurting and I was cramping here and there for a while then it stopped. Yesterday my nipples hurt to the touch but that has stopped. I was supposed to get my period yesterday but I didn't and I still have not today. I don't know I feel like I'm probably getting my period but I'm not sure or is it implantation bleeding? Help??