Pregnant?

My last period was Jan. 6, usually i have a 29 day cycle so it was due Monday, now its friday and not here! i have felt kind of sick the past couple of days but other than that no other symptoms. I took a hpt on Wed. and it was negative. should i take another? ive had some headaches on and off and my mouth seems to have extra saliva..dont know if that has any thing to do with it but just in case! thank you