Why Are My Menses Late After Weaning Of BC Pills?

I was using the implanon contraceptive implant for 22 months, I had it removed 6

weeks ago as my husband and I wish to start a family. 5 days after removal I

had 1 day of bleeding.

I am now almost a week late for my period. I have tender nipples and breasts,

occasional feelings of nausea and lightheadedness and cramping. I have taken 2

pregancy tests both have come back as negative, so I would like to know if I am not pregnant then why is my period so late?