very bloated and had unusual food cravings...

me and my partner have been having un protected sex for the last few weeks and i have been very bloated had unusual food cravings had back ache been frequently urinating
i have taken many pregnancy tests but they have all come back negative is there still a chance i could be pregnant i was due on on 24th match and my period is still a no show plz give me some advice
i have also noticed in the ast 2 days that i have had ery light menstrual bleeding but only little tiny bits and only once a day