What Causes A Delayed Period With Negative Pregnancy Test?

I had an atypic amigraine earlier,with photo/phono sensitivity,nausea that lasted most of the morning. It continues now,despite taking my prescribed med,meclofen,and feels more like intense pressure on top of and in back of head. Also, breastfeeding and 8 weeks late with period,with a negative test 2 weeks ago,as well as low grade fever,99.4. Any suggestions?