Help .... could i be pregnant ?? i slept with my bf 6 days ago but i was due for my period four days ago?

i slept with my bf for the first time 6 days ago we did not use protection... i was due for my period four days ago and i have not got them.... i had taken a preganice test yesterdai bout it was NEGg?? my periods are alwais 28 days cycle and neva late my were not sore untill this morning ... could i be pregnant??