I don't think so but could I be pregnant?

Ok so I was suppose to start my period aug 21st give a day or to. well 8 weeks later and no period. I have taken test and they all say no. I called the nurse line here and she said to wait a little longer and retest my self. I am tired my lower back hurts and just the nipple is tender and just a little at that. Could some one give me advice please.