How correct are digital pregnancy tests?

I've been reading a lot lately that woman have received positive pregnancy tests but when they do a digital test its negative, I did a pregnancy test at 5 days to period and got negative digital pregnancy test but I just don't feel right since 6 days till my period I have been getting slight cramping ,bloating and slightly swollen breasts! WHICH since my period first started I have never got until the time my period comes! Help?