What Causes Missed Period, Nausea And Ribs Pain While HPT Is Negative?

I missed my period 4 months ago, had a bit of spotting in the begining of aug. and it didnt even seem like a usual period and im 8 days late on what should be a regular period this month. i have done a blood test and a home and med urine test and still negative. ive been nausaus, weird eating, tired and severe pain in my left side by my ribs. is this pregnancy?