Late for period... Negative test

I normally have a regular 28 day cycle. Last month I wAs 3 days early, and started period on 7th january. however this month I've still not started my period :/ I haven't had any of the signs of AF, like cramps sore boobs and pms! I know it's only a couple of days but I took a test last night and it was negative. Wondering how long to leave it till I take another?